Theory Galaxies

First galaxies observed were simply called "spiral nebulas," because it wasn't known how far away they were. It was not until the discoveries of Edwin Hubble, in the early 20th century, that galaxies were seen like other island cities of stars far outside our Milky Way Galaxy. Knowledge of galaxies' early history is impeded due to time zones where they are dwelling, being at the limit of our astronomical tools. Two main theories now are accounting for galaxies' history: "co-evolution", which is linking galaxies and black holes; "Collisional Starburst Scenario" which thinks that galaxies are forming, merging smaller stellar groups. Two additional concepts -the role of dark matter, a further role of collisions and mergers- come along with these theories. The collisional theory likely is a major explanation, as, for every major encounter between two spirals there are probably up to 10 times more frequent clashes between a large and a dwarf one. Even elliptical galaxies, for example, may regain some vigor in terms of star formation through encounters with dwarf galaxies. NGC 300 is a such a good, textbook representation of a spiral galaxy that astronomers have studied it in great detail to learn about the structure of all spirals in general as, at about 39,000 light-years across, NGC 300 is only about 40 percent the size of the Milky Way Galaxy. Lightest galaxies are around a billion solar masses, while the heaviest are 30 trillion

->Easier Still!
A fully developed elliptical galaxy is finally the result of a gas-deficient gathering of ancient stars theorized to develop from the inside out, with a compact core marking its beginnings. Such early galactic cores already contain about twice as many stars as our own Milky Way Galaxy into regions as small as 6,000 light-years across. Such a density is allowed due to the early Universe being more compact than nowadays as galactic cores then yield about 300 stars per year. These are very extreme environments with a lot of turbulence and bubbling. The process likey is sparked by a torrent of gas flowing into the galaxy’s core while it formed deep inside a gravitational well of dark matter. After that early episode, mergers between galaxies brought those ancient ones to more sedate ones

->Let's Make it Easy!
Albeit this domain in astronomy is still largely in the making -the very beginnings of stars and galaxies being still hidden to astronomers or just at the limit of the current tools- here is an easy explanation of how things might have started! First, first generation stars formed. They did from the collapse of hydrogen and helium gas clouds and worked then during a few million years only. They quickly ended like supernovae, in turn producing a black hole. Such supernovae, on the other hand, enriched the medium with heavy elements like carbon, oxygen, and silicon, which were the seeds for next generation stars and planets. A 'halo' of dark matter, further, acted as a seed for the collection of first and second generation stars, black holes, gas and dust, bringing to the formation of first proto-galaxies, at the center of which gas, stars, black holes and other stellar remnants accreted together, forming a massive black hole, featuring two energetic jets (when one of these jets is pointed to us, we see a quasar). The haloes of dark matter can represent up to 80 percent of a galaxy's mass as their existence was originally proposed to explain why the outer parts of galaxies are rotating unexpectedly fast. It's the collisions and mergers between these proto-galaxies which formed after that the most usual larger galaxies by a series of constructions. Spiral galaxies are thought to build when the inflow of material was -still is- smooth and is gas mainly, as elliptical galaxies were/are due to more violent, head-on events. Dark matter is thought now to be a necessary ingredient to the formation of any galaxy or quasar. More marginal types of galaxies either don't need any heavy elements, or even any dark matter. Recent studies found that some dwarf galaxies might have formed from the early Universe material and not needing any dark matter nor the metals -or 'heavy elements', elements beyond the helium- which were produced by the first-generation stars. Tidal dwarf galaxies, on the other hand, are galaxies which form building upon the collision between two large galaxies, with material spread around are building upon heavy elements which have been thus cycled through an existing galaxy, but they don't need any dark matter as that one has just been teared off due to the collision. A study by late 2011 has found that young dwarf galaxies, 9 billion years ago, were brimming with star formation as their stellar content would double in just 10 million years. By comparison, our Milky Way Galaxy would take a thousand times longer to double its star population. Such a formation rate is extreme even for the young Universe. The reason why is still unknown as dwarf galaxies seen nowadays have come to a more normal star formation rate. In terms of the influence of their supermassive black hole, studies have shown that galaxies with the most powerful, active, supermassive black holes produce fewer stars than galaxies with less ones. Data suggest that galactic black holes and the stars in their host galaxies grow in tandem with each other but biggest black holes in the most massive galaxies were found growing faster than the rate of stars being formed in their galaxies. Maybe massive galaxies are more effective at feeding cold gas to their central supermassive black holes than less massive ones. The growth of most massive black holes on the other hand, outstrips that of stars. The mass of galactic black holes, generally, is connected to the X-ray and radio emission. Such that ratio might result either from a head start or from a edge in growth acquired over billions of years. Star formation and black hole activity increase together, but only up to a point as radiation spewed eventually prevents raw material from coalescing into new stars

->The Latest Conception About Galaxies Formation!
NASA Galex mission recently, in 2007, came to the conclusion that the 'nurture' theory might be the last word about how galaxies are evolving along their life. According to those views, a typical young galaxy begins life as a spiral which is actively churning out stars, as it further merge with other spiral or irregular galaxies -leading to some bursts of stars formation- and, eventually, the galaxy settles into an elliptical through fuel exhaustion and perhaps suppression by black holes. A major consequence of such a finding is that astronomers today, tend to talk about galaxies by referring to them by their color (blue for small or irregular galaxies, red for large ellipticals), instead of their shape, like previously done. Those recent discoveries further proved that an intermediate-class, 'teen' galaxies fills the gap between young, and older galaxies. Some of those mid-age galaxies are ripening into old quickly, while others are lingering a long time in their state. Astronomers, on a other hand, recently understood that galaxies in the early universe continuously ingested their star-making fuel over long periods of time, in the order of periods of hundreds of millions of years, and having a strong large, hot and bright-stars rate formation as previous theories stated that the galaxies devoured their fuel in quick bursts after run-ins with other galaxies. The merging of massive galaxies was not thus the dominant method of galaxy growth in the distant universe. H alpha, which is radiation from hydrogen gas that has been hit with ultraviolet light from stars hints to that. A missing link population of galaxies found by NASA's Galex mission about 2012, is showing how the two major types of galaxies in our Universe -the 'red and dead' ellipticals and the blue spirals- can transition from one type to another as galaxies indeed don't have a single personality, but look like they may change types many times over their lifetime! From surveys of non-dusty galaxies from dusty ones, astronomers have a different picture as both pictures don't always match. picture courtesy NASA/JPL-Caltech

A process might be common and essential to understanding galaxy formation, with cold gas falling towards a supermassive, galactic black hole, igniting the black hole and causing it to launch fast-moving jets of incandescent plasma into the void and the galaxy’s gravitational clutches and plasma cooling off and slowing down, eventually raining back down on the black hole, where the cycle begins anew. The physics of star formation and the deposition of mass, momentum and energy into the interstellar medium by massive stars are the main uncertainties in modern cosmological simulations of galaxy formation and evolution. These processes determine the properties of galaxies. In simulations, the timescale for depleting molecular gas through star formation in galaxies (about 2 billion years), exceeds the cloud dynamical timescale by two orders of magnitude

From left to right: a young, blue, stars forming galaxy, a 'teen' one, and an older, elliptical, red galaxy picture site 'Amateur Astronomy'

First Stars and Galaxies. ab. 200 Million Years After the Big Bang The Quasars Era. 1 Billion Years After the Big Bang The Proto-Galaxies Period. 1.4-4.6 Billion Years After the Big Bang

Usual Galaxies. Starting at 4.5 Billion Years After the Big Bang More Data

First Stars and Galaxies. ab. 200 Million Years After the Big Bang

The first 500 million years of the universe's existence, from a z or redshift of 1000 to 10, is, for the astronomers, the missing chapter in the hierarchical growth of galaxies. It's not clear how the Universe assembled structure out of a darkening, cooling fireball of the Big Bang. Astronomers know there must have been an early period of rapid changes that would set the initial conditions to make the ensemble of galaxies what it is today. The rate of star birth then in the early Universe grew dramatically, increasing by about a factor of 10 from 480 million years to 650 million years after the Big Bang when stars and first clumps of those formed from gas trapped in pockets of dark matter. Astronomers suspect that there is a abundant, underlying population of extremely small, faint objects at 500 million years after the Big Bang, with size of 850 light-years across only and masses of 40 million stars. Such galaxies are swiftly turning then to a strong star formation. Some smaller galaxies managed to travel through history while remaining pristine, and never bulked up in heavy metals, remaining metal-poor galaxies like when the first stars formed. The first-ever stars from billions of years ago took root in poor conditions, with no heavy metals extant which act like a fertilizer. 'Big baby' galaxies are galaxies much larger and more mature than scientists thought early-forming galaxies could be

Earlier Galaxies and Clusters: the MACS0647-JD dwarf galaxy was, as of late 2012, the oldest object surveyed in the distant Universe at a 420 million years after the Big Bang only and possesses a redshift of 11. Other galaxies have been found mature, with heavy elements, at only about 700 million or even 530 million years, after the Big Bang. Embryonic galaxy named SPT0615-JD, which existed when the Universe was just 500 million years old is seen in more details because of a gravitational lens. Star formation have been found latter in a early galaxy to start only 250 million years after the Big Bang, which makes that galaxy -- MACS1149-JD1, in constellation Leo, the Lion -- the most distant observe too. As no oxygen existed in the early Universe, it's the first star death process which provided for. Such data are considered earlier than usually admitted. The farthest galaxy group is a trio of galaxies at 680 million years after the Big Bang. A mature galaxy cluster XLSSC 122, with 37 member galaxies, was detected at redshift 2, or at 10.4 billion years ago

It begins to be admitted that stars and galaxies are forming at an important rate very early in the Universe. This occurs as soon as before the end of the "Dark Ages" that is when Universe, beginning at 400 million years after the Big Bang, is mostly invisible to us due to neutral hydrogen blocking light of very first objects. First stars have been seen as far away as just 200 million years after the Universe began. First observed galaxy has been seen at 1 billion years after the Big Bang, that is 12.7 billion light-years from us! It's a group of one million stars, 1/20th our Galaxy in size, as more were found in 2007, small in size and composed of active, young, blue stars turning hydrogen and helium into heavier elements. Further studies however by 2015 showed that small, primordial galaxies in the early Universe are in number, being more diffuse and populated by giant stars than thought. Galaxies, owning about one billion stars, formed as soon as by 600 million years after the Big Bang and containing dust clouds and oxygen, the results of supernovae explosions. Gamma-ray burst is seen some 100 million years later. Such objects thus are living fully within the so-called epoch of reionization between about 150 million to 800 million years after the Big Bang. One of the most dramatic impacts galaxies have had on the whole history of the universe is through reionization. Such tiny galaxies could have been the primary sources of ionization during this epoch, the researchers suggested. A bubble of ionized hydrogen gas at least 6.5 million light-years wide is surrounding UDFy-38135539, a width not allowed by galaxy's weight only, hinting to fainter and less-massive companion galaxies. Such primeval galaxies are the building blocks from which further galaxies form as mergers also include cold gas. It's there that first stars are forming. Cold dark matter is thought to play a role in these processes as these first galaxies are merging into larger galaxies inside dark matter halos. These mergers are yielding a higher rate of star formation. The "Central Quiescent theory", which thought that galaxies were forming by slow accretion had now been almost completely discarded. Stars successively formed in a star formation environment are getting progressively bluer at each generation due to that they benefit from heavier elements formed by the very first generation of them, mostly helium. Most recent studies are showing that those primeval galaxies may turn either into larger elliptical, or spiral, galaxies as it might that Nature’s apparent preference for spirals exists. Galaxies do not always need to collide with each other to drive vigorous star birth on a other hand. In the early Universe, when most galaxies contained a lot more gas than later albeit not good at forming stars, mergers were not the only way, or even the most common way, to make lots of stars at a rapid rate. That also could occur when a galaxy kept accreting gas material still lying around it. Early galaxies, on a other hand, might have been of a important size already and forming stars at most high rates, like one found at a mere 750 million years after the Big Bang, or a redshift 7.2, forming a hundred Suns per year (compared to 3 in the current Milky Way Galaxy). It is blob-shaped with a size five times smaller our Galaxy and a mass 100 times smaller. Most luminous galaxies exist at 12.5 billion years ago, shining with the light of more than 300 trillion Suns, objects called 'extremely luminous infrared galaxies, 'or ELIRGs as they might harbor a behemoth black hole gorging itself on gas. The discovery by early 2013 that dwarf galaxies around the Andromeda Galaxy are rotating about it and are displayed in a planet seems contradictory with the theories of galaxies' formation and dark matter. Dwarf galaxies, according to those, should be the remains of original populations which agregated randomly through dark matter to form galaxies. As Andromeda's dwarf galaxies orbit on a same plane, that discovery is the first confirmation of a intuition which already existed and claimed that dwarf galaxies located in the vicinity of larger structures were not randomly shared out. Astronomers now have to resolve such a contradiction as some even goes up to pretend that the physics of Einstein and Newton are not correct. Andromeda's galaxies are grouped unto a thin plane of rotation, which is about perpendicular to M31. Elongated, small-sized galaxies exist in abundance during the earlier epochs of the Univers, and drifting into space, which made that intergalactic gas rained unto and triggered a frenzied star formation. About 10 percent of all galaxies at the time have these elongated shapes, and are collectively called 'tadpoles.' The development of them lagged behind that of their peers which turned spirals during billions of years

In a key step to understand how dark matter is contributing to the birth of galaxies in the early Universe, the Herschel Space Observatory, a joint ESA-US mission was able to determine how much such matter is needed to that a star-forming galaxy be born! The right amount of dark matter turns out to be a mass equivalent to 300 billion of our Sun. Starting with too little dark matter, then a developing galaxy would peter out as if too much, then gas doesn't cool efficiently to form one large galaxy, and ends up with lots of smaller galaxies. A primeval galaxy-making process works like giant clumps of dark matter act like gravitational wells that collect the gas and dust needed for making galaxies. When a mixture of gas and dust falls into a well, it condenses and cools, allowing new stars to form. Eventually enough stars form, and a galaxy is born. Early galaxies are more clustered into groups than previously believed as the amount of galaxy clustering depends on the amount of dark matter. Galaxy groups on the other hand, are some of the most common galactic gatherings in the cosmos, and they comprise 50 or so galaxies all bound together by gravity. The observation was made about star-forming galaxies located 10 to 11 billion light-years away, in a region of the sky called the 'Lockman Hole,' located in the constellation of Ursa Major. A huge galaxy protocluster forming in the early Universe, on a other hand, revealed that a lot of star formation is occurring hidden behind dust inside the cluster self. Precursors of galaxy clusters have been found in a 3-billion years old Universe as a protocluster even was observed at 1 billion years after the Big Bang. Stars and galaxies sprung to life in the early universe, only later assembling into large clusters. The formation time of galaxy clusters is at about 11.1 billion years ago. A large amount of hot gas is one of the defining features of a galaxy cluster. Once the clusters formed, massive amounts of matter collapsed under the influence of gravity, triggering the formation of new stars and galaxies. Dark matter was intermingled with the stars and galaxies, and helped usher along the process of creating stars

Most powerful supernova explosions of massive stars are happening nowadays in extremely low-mass galaxies. Stars that start out massive in these little galaxies stay massive until they explode, while in larger galaxies they are whittled away as they age, and are less massive when they explode. Such little galaxies are low in mass and have low rates of star formation. They tend to have fewer heavy atoms, such as carbon and oxygen, than their larger counterparts as these small galaxies are younger, and thus their stars have had less time to enrich the environment with heavy atoms. Such a lack of heavy atoms in the atmosphere around a massive star causes it to shed less material as it ages. In essence, the massive stars in little galaxies are fatter in their old age than the massive stars in larger galaxies. And the fatter the star, the bigger the blast that will occur when it finally goes supernova. Such dwarf galaxies are quite similar to the kinds of galaxies that may have been present in our young Universe. Lyman-alpha emitters are galaxies that shine only in Lyman-alpha hydrogen line, as current understanding of star formation cannot fully explain these galaxies. Luminous hydrogen halos exist around galaxies in the early Universe, hinting to material flows in and out of early galaxies

->Dwarf galaxies seen around major galaxies in the Universe today are thought now to be the building blocks of them. Much dwarf galaxies, that way, are lurking inside galaxy clusters. Such galaxies are of the size of the Small and Large Magellanic Clouds, those satellites to our own Milky Way Galaxy, and probably related to those first primeval galaxies as described above
A study in the summer of 2007, on the other hand, has found the most earliest galaxies ever seen, at 500 million years only after the Big Bang, likely being some of those objects which participated into re-ionizating the neutral hydrogen of the 'Dark Ages'

->Galaxies Appearing in the Web Universe's Filaments
A recent, 2008, breathrough in the knowledge of how galaxies are forming occurred, with the astronomers now thinking that galaxies are forming into the filaments of the Web Universe, and then moving from there to the nodes of it, there where the galaxy clusters are found!
The Universe now is thought of like being an ensemble of vast filaments of hydrogen linking at nodes, making the Universe resemble like a vast sponge of sort

->Another View of the Role of the Earlier Black Holes Relatively to The Galaxy Formation!
Through a computer modeling, a study, in 2009, found that the earliest black holes lacked nearby matter to gobble up, and so they lay relatively stagnant in pockets of emptiness. That counters the earlier idea that the first black holes had accumulated mass quickly and ballooned into the supermassive, galactic black holes. This is explained as first stars, which formed with the earlier gas of the gas clouds, were very large stars of about a hundred solar masses, as they swiftly formed black holes after their end into a supernova. Those stars however, through their very strong radiations, emptied their surrounding space of any matter hence the black holes lacked anything to feed on, increasing in size by one percent by 100 million years only! Their role into the formation of the earliest galaxies however remains as they are strong X-rays emitters and affecting faraway gas into prohibiting the star formation there for cause of the generated heat! Such gas clouds which did not turn into stars later collapsed about themselves, after millions of years and would thus have directly create the supermassive black holes. The original, unfeeding black holes, as far as they are concerned, would have either be absorbed into orbit by larger objects which later themselves turned into black holes, or they might be still extent today, with their original size in the halos of the galaxies, as they would have been ejected there through gravitational interactions with the other objects of their galaxies. Central black holes now are usually thought to have formed at a early stage in galaxy evolution and in small galaxies

By 2011, using a picture taken in the ultraviolet by the Chandra X-ray Telescope, astronomers have obtained the first direct evidence that black holes are common in the early Universe, between about 800 and 950 million years after the Big Bang, and shown that very young black holes grew more aggressively than previously thought, in tandem with the growth of their host galaxies. Black holes formed as small seeds in the early Universe and grew by swallowing stars and gas in their host galaxies, merging with other giant black holes when galaxies collide, or both. Although a population of young black holes in the early Universe had been predicted and evidence for parallel growth of black holes and galaxies has been established at closer distances, the new Chandra results show that such black holes exist and that this connection started early, perhaps right from the origin of both. Between 30 and 100 percent of such early galaxies contain growing supermassive black holes bringing to a total of at least 30 million supermassive black holes in the early Universe. Such early supermassive black holes are to grow by a factor of about a hundred or a thousand, eventually becoming like the current giant black holes, almost 13 billion years later. Enormous gas halos around the earliest galaxies in the Universe, at about 12.5 billion years ago and extending 100,000 light-years from the galactic centers, are the perfect food for supermassive black holes at the centre of these. That gives a explanation to the rapid growth of quasars at the time. The number of black holes thus in the early Universe amounts to 10,000 larger than the estimated number of quasars. At the same time as they are less extreme versions of quasars -which, as far as they are concerned, are very luminous, rare objects powered by material falling onto supermassive black holes- as about a thousand times less massive than the ones in quasars. All such early galactic black holes are enshrouded in thick clouds of gas and dust as optical light generated by material falling onto the black holes is blocked within the core of the host galaxy and is detectable in the high energies of X-ray light only. Astronomers further though that early black holes would play an important role in clearing away the cosmic 'fog' of neutral, or uncharged, hydrogen that pervades the early Universe when temperatures cooled down after the Big Bang. However, the Chandra study shows that blankets of dust and gas stop ultraviolet radiation generated by the black holes from traveling outwards to perform such that 'reionization.' Therefore, stars and not growing black holes are likely to have cleared this fog at cosmic dawn

The Cosmic Evolution Survey (COSMOS) survey of the sky by the Spitzer Space Telescope turned up, in 2014, hundreds of hefty galaxies 100 times the mass of our own Milky Way, dating back to a time when our Universe was less than one billion years old, casting doubt on current collisional models of galaxy formation. How these remote and young galaxies grew so big so fast. A alternate explanation for that could be that galaxies started to form about 400 million years after the Big Bang, which is a hundred million years earlier than thought

The Quasars Era. 1 Billion Years After the Big Bang

A quasar, specifically, is the compact region which surrounds a supermassive black hole in the center of a active galaxy. The majority of supermassive black holes in the early universe might be cloaked by dust. Some astronomers think that the presence of much dust was the main cause of the peek of stars formation in galaxies during that period -- and then the absence for their decline as stellar radiation and winds, supernova explosions, and possible galactic supermassive black holes' jets also may have been a factor. Radiation emitted by feeding black holes in a quasar, with their speed and temperature, may be ripping their galaxy apart, and/or stunting star formation. The era of those early galaxies is better known since ESA's Herschel Space Observatory (launched by 2009 and terminated since) which resolved the cosmic infrared background radiation into galaxies. A critical stage in the evolution of galaxies is about a billion years after the Big Bang as even hyper-starburst galaxies could exist at the time. The farthest known supermassive black hole, with 800 million solar masses, is a quasar lying by 690 million years after the Big Bang -- at a redshift 7.54 -- and large and remaining in a pocket of neutral hydrogen, or the only example we have that can be seen before the universe became reionized. For black holes to become so large in the early universe, astronomers speculate there must have been special conditions to allow such a rapid growth. Astronomers think that 20 to 100 quasars as bright and as distant as this quasar exist as latest studies are showing that very bright quasars are not that numerous indeed in the early Universe. A quasar is characterized by a accretion disk around emitting up to a thousand times the energy output of the Milky Way. Magnetic reconnection happens in quasars like in many places in the Universe, or nuclear reactors. Galaxies were then more efficient at making stars when the Universe was younger, ranging from 0.75 to 1.5 billion years after the Big Bang (or between redshift 4 and redshift 7). That likely is due to that, at earlier times the Universe was packed closer together, including the gas in galaxies as galaxies also might have experienced less 'feedback,' or different barriers causing the gas not to form stars. No galaxy is 100 percent efficient at turning gas into stars as there are several mechanisms inside galaxies that can cause some of the gas to not form stars, like the massive explosions called supernovae, winds from massive stars, and active supermassive black holes that can heat their surrounding gas as such barriers are collectively called 'feedback.' The growth of black holes linked to the formation of stars (with heated gas stopping stars formation), a percentage of 0.2 to 0.5 percent of a galactic black hole's mass relative to its parent-galaxy, did not work in the early Universe like in today's as black holes might have grown more efficiently than galaxies in the early Universe, with values at 10 percent. Supermassive black holes not only ingested large quantitites of gas and dust as they may also re-emitted gas outward. Large cavities and filaments existed in the hot gas around many massive galaxies. A explanation to numerous supermassive black holes in the early Universe is a theory stating that some supermassive galactic black holes might have like a origine the collapse of supermassive stars, with masses around 10,000 times that of the Sun. Such stars themselves owe their origin to regions where galaxy formation occurred swiftly, which in turn is seen where a dark matter halo is growing rapidly. Such black holes thus occur before galaxies do 0.2. X-ray binaries also might have played a role in the evolution of our Universe as they might have played a critical role in heating the intergalactic bath of gas in which the very first galaxies formed. The speed at which some galactic black holes developed in the earlier Universe, on a other hand, might be due to the disruption of large stars and the fact that they gorged a longer time upon

Recentest Views About Quasars!
The peak of quasar activity in the early Universe was definitely driven by galaxies colliding chaotically and then merging together, which fed supermassive central black holes with gas. Discovered in the 1960s, a quasar pours out the light of as much as one trillion stars from a region of space smaller than our solar system. Quasars are the most active of galactic supermassive black holes, with infalling material heated to a point where a brilliant searchlight shines into deep space. That beam is produced by a disk of glowing, superheated gas encircling the black hole. Quasars are supermassive black holes with masses ranging from millions to billions of times the mass of the Sun and residing at the centers of galaxies. They can gobble up huge quantities of gas and dust that have fallen into their gravitational pull. As the matter falls towards these black holes, it glows with such brilliance that they can be seen billions of light years away. The disk of matter surrounding a quasar may be thin or thick depending on how the black hole is gorging on matter

Quasars -short for quasi-stellar object' as, when they were discovered such objects looked like stars but their true nature ill-known- are the brightest objects in the Universe and are the brilliant cores of 'active galaxies' that contain a active central black hole. Infalling material fuels a super-massive black hole and more especially both jets escaping from the disk surrounding the black hole and shining in the Earth's direction. The energy released as particles fall toward the black hole generates intense radiation and powerful beams of high-energy particles that blast away from the black hole at nearly the speed of light. These particle beams can interact with magnetic fields or ambient photons to produce jets of radiation. As the electrons in the jet fly away from the quasar, they move through a sea of background photons left behind after the Big Bang. When a fast-moving electron collides with one of these so-called cosmic microwave background photons, it can boost the photon energy into the X-ray band. That occurs with quasars which exist when the cosmic background radiation is a thousand times more intense than it is now, making the jet much brighter. On a other hand, X-ray jets during such remote times appear to be moving slightly more slowly than jets from galaxies that are not as far away. This may be because the jets were less energetic when launched from the black hole or because they are slowed down more by their environment. Active galaxies are galaxies emitting gamma rays as such a unusually bright center shows evidence of particle acceleration to speeds approaching that of light. A quasar existing just 1 billion years after the Universe began has been seen by NASA's Chandra X-Ray telescope harbouring a supermassive black hole, like other, older, quasars are doing. This is of importance as this is the evidence that all quasars, whatever their age, are powered by such supermassive black holes. How does such massive black holes appeared so swiftly? It might that such black holes are due to the merger of thousands of stellar black holes, themselves due to massive stars' supernovae events. The black hole in SDSSp J1306 is a billion solar-mass worth! Such black holes have a similar shape. Infalling matter is producing a rapidly rotating "accretion disk", and a hot atmosphere (a "corona"). A part of the high-energy X-rays emanating from such events is due to low energy optical, UV, and X-ray photons coming from the accretion disk and bumping into hot electrons in the corona. The photons are then boosted up to the higher-energy X-ray range. Quasars date back to a time in the Universe's history which held large amounts of dust as some underlying galaxies may be dusty to the point that their galaxies are not seeable. Quasar winds significantly contribute to mass loss in a galaxy, driving out its supply of gas, which is fuel for star formation picture courtesy X-ray: NASA/CXC/D.Schwartz & S.Virani; Illustration: CXC/M.Weiss

->A recent study is showing that a galaxy formation bloom occurred around 900 million years after the Big Bang as, barely earlier in time, nothing similar is seen. It seems likely that such a bloom might be linked to the 'quasar era'. Galaxies, at about 1 billion years after the Big Bang are dwarf galaxies, as they are producing stars at a rate ten times higher than galaxies that come after that time

The earliest quasars have been found by 2010, at a distance of 13 billion light years ago, and weighing more than 100 million Suns! A black hole of 12 billion solar masses has been found in a galaxy just 875 million years after the Big Bang, at 3000 times the size of our Milky Way’s galactic black hole. To have grown to such a size in so short a time, it must have been munching matter at close to the maximum physically possible rate for most of its existence. Such early quasars are seen in a epoch of the Universe when no any molecules that could coagulate for form dust was existing, which eventually formed by the generations of stars exploding into a supernova. The mass of the supermassive black hole self is another factor as the longer a black hole grows, the more dust has time to materialize around there. As devoided of dust, those early quasars are thus easier to spot deep into the past. Quasars are very bright, faraway, objects thought to be supermassive black holes located in the center of galaxies and outshining them. According to the co-evolution theory, black holes and galaxies develop interacting as they compete for matter from the original gas clouds. Black holes might also appear in building-block galaxies of the previous period, as they would become active only during this second epoch. Like those of today, supermassive black holes are at 75 percent shrouded into thick envelopes of dust. A stronger correlation has been established between the size of black holes and the size of dark matter halos. During this period are found too "infrared" galaxies which are forming stars at an important rate. The average lifespan of stellar black holes' accretion disks are about 100 million years, with some local, special conditions, sometimes reducing that to 2,000 years only. This epoch too keeps having building-block galaxies, with some observed by the Hubble Space Telescope to be tiny, at about 100 or a 1,000 times smaller than our Milky Way Galaxy. A lot are seen slightly disrupted, possibly a sign that they are interacting. The study of faraway galaxies in the infrared, through the Spitzer Space Telescope, is showing that most galaxies are featuring a supermassive black hole, and that the number of quasars might be much higher than estimated now. Another recent discovery might be too that the quasars' supermassive black holes themselves might be at the origin of dust, and not only supernovae events. European ESO have discovered the most powerful quasar, SDSS J1106+1939, with jets of approximately 400 times that of the Sun is streaming away from this quasar per year, moving at a speed of 5000 miles per second (8000 kilometres per second). Why there are so few large galaxies in the Universe could be linked to the quasar era, with powerful jets emanating from those. The regulation of the largest black hole and their host galaxies works is like that, in some galaxies, hot gas is able to quickly cool through radiation and energy loss, in a process called precipitation. The clouds of cool gas that result then fall into the central supermassive black hole, producing jets that heat the gas and prevent further cooling. In some galaxies, the intense heat likely shut off the precipitation around the black hole, or, with a same result, strong bursts of outflows from regions near the black hole. The gas displaced under the influence of a black hole, generally, is cooling

Galaxies' supermassive black holes might have formed first like black holes, through large galaxies' mergers, as soon as by 1 billion years after the Big Bang. Astronomers discovered by late 2014 that the rotation axes of the central supermassive black holes in set of quasars forming huge groupings, are parallel to each other over distances of billions of light-years as the rotation axes tend to be paralleled with the vast structures of the cosmic web, maybe a hint that there is a missing ingredient yet in our current models in the Universe. Galaxies in the early Universe typically contain hydrogen gas glowing under the ultraviolet radiation from hot young stars. Our current knowledge of cosmic star-formation history during the first two billion years is mainly based on galaxies identified in ultraviolet light. However, this population of galaxies is known to under-represent the most massive galaxies, which have rich dust content and/or old stellar populations. This raises the questions of the true abundance of massive galaxies and the star-formation-rate density in the early Universe. Although several massive galaxies that are invisible in the ultraviolet have recently been confirmed at early epochs, most of them are extreme starburst galaxies with star-formation rates exceeding 1,000 solar masses per year, suggesting that they are unlikely to represent the bulk population of massive galaxies. A bulk population of massive galaxies that has been missed from previous surveys contribute a total star-formation-rate density ten times larger than that of equivalently massive ultraviolet-bright galaxies as they are residing in the most massive dark matter haloes, being probably the progenitors of the largest present-day galaxies in massive groups and clusters. Galaxies in the early Universe typically contain hydrogen gas glowing under the ultraviolet radiation from hot young stars

The Proto-Galaxies Period. 1.4-4.6 Billion Years After the Big Bang

A pristine cloud of gas, devoided of any heavy elements, has been observed at 1.5 billion years after the Big Bang. Faint dwarf galaxies residing between 2 and 6 billion years after the Big Bang were responsible for forming a large proportion of the Universe's stars, and at such a rate they could actually double their entire mass of stars in only 150 million years. Gigantic galaxies at 12.5 billion years ago are obscured by a warm glow of dust, which explains why steps of growth of those galaxies in the early Universe are not seen. A dwarf galaxy containing a plentiful reservoir of gas may not produce stars as a nearby giant spiral may be stealing gas from it. As galaxies merge, newly-formed stars feed on their combined gases, and exploding stars and supermassive black holes emit galactic material, a process that depletes the mass of a galaxy. Such 'starburst galaxies' form stars at a furiously fast rate as they usually are the result of an unusual incident in the past, such as a violent merger. There is a much high proportion of massive stars within starburst galaxies. Collisions of young, starburst galaxies occurred as soon as 1.5 billion years after the Big Bang as such systems of galaxies are thought to form the core of first galaxy clusters. A galaxy proto-supercluster has been observed as soon as at 2.3 billion years after the Big Bang as superclusters are closer in time to use, because the Universe had to take time to build such large structures. Proto-superclusters do not feature concentrated distribution of masses in denser regions, for the same reason. Three billion years after the Big Bang galaxies still made stars on their outskirts, but no longer in their interiors. The quenching of star formation seems to have started in the cores of the galaxies and then spread to the outer parts. The fraction of the Universe's hydrogen and helium gas that was involved then was very low. Today, star birth is happening at a much slower rate than long ago, but there is so much leftover gas available that the Universe will keep cooking up stars (and planets) for a very long time to come. Since about 2010, astronomers discovered a population of small, but massive galaxies called 'red nuggets,' with black holes there having squelched star formation and used some of the untapped stellar fuel to grow to unusually massive proportions. Some compact elliptical galaxies might be the descendants of the red nuggets and they might pack a lot of dark matter concentrated in their center. Such galaxies are located by some three or four billion years after the Big Bang. They are relics of the first massive galaxies that formed within only one billion years after the Big Bang. Astronomers think they are the ancestors of the giant elliptical galaxies seen in the local Universe. The masses of red nuggets are similar to those of giant elliptical galaxies, but they are only about a fifth of their size. Most red nuggets merged with other galaxies over billions of years

->Varied Classes of Active Galaxies
Active galaxies, generally, emit radiation across the complete electromagnetic spectrum, from radio waves to gamma rays, produced by the action of a central supermassive black hole that is devouring material getting too close to it. AGNs exist over a large range of activity, from galaxies like NGC 4639 to distant quasars, where the parent galaxy is almost completely dominated by the emissions from the AGN, or a supermassive black hole. The 'unified model of AGNs' is the assumption that rotating donut-like structures of dusty gas are found around active supermassive black hole. AGNs are so bright because particles in the regions around the black hole get very hot and emit radiation across the full electromagnetic spectrum -- from low-energy radio waves to high-energy X-rays. However, most active nuclei are surrounded by a doughnut-shaped region of thick gas and dust that obscures the central regions from certain lines of sight. Active galaxies may be found as close as by 170 or 38 million light years from us. As blazars and radio galaxies are the most known of the active galaxies -those galaxies emitting gamma rays and with unusually bright centers that show evidence of particle acceleration to speeds approaching that of light, and that both classes were first described by astronomer Carl Seyfert in 1943, astronomers now believe that those two classes represent the same phenomenon seen at different viewing angles and additional classes are extant. Some, for example, are producing strong and variable radio emission (as the brightness of the galaxies at radio wavelengths shows that they contain stars forming at high rates), or changes in the output suggest that the particles beams endure period of activity, or inactivity. Active galaxies are generated due to that, at their center, sit a feeding black hole as the nurture blasts outward in fast, oppositely directed particle jets, with the blazars being jets astronomers are looking right down the particle beam! Blazars generally are a voracious supermassive black hole inside a galaxy with a jet that happens to be pointed right toward Earth, a rarity. Blazars are among the most energetic objects in the universe, beaming in the gamma rays. They consist of supermassive black holes actively pulling matter onto them, at the cores of giant galaxies. Electrons, protons and other particles accelerated in blazar jets leave a specific fingerprint in the infrared light they emit. A same pattern is also clearly evident in their gamma rays, a sign that blazars convert matter around in gigantic amounts of energy. All those 'Active Galactic Nuclei', or AGNs, are actively star-forming galaxies found at varied distances in the Universe. Galaxies, generally, that are actively forming stars have a distinctly bluish color (they are 'blue and booming), while those not doing so appear quite red. AGNs, on the otherhand, are mostly massive "red and dead” galaxies where they are located 7 billion years away from us. When closer, for example within 600 million light-years their colors fall midway between blue and red. Galaxies nicknamed 'red and dead' stopped producting stars some 10 billions years ago as the halt likely happened when the galaxy gobbled up surrounding galaxies. Such galaxies also hold large galactic black holes which grow along with a flurry of stars. Such galaxies usually are found in the early Universe only. Approximately one in 1,000 massive galaxies is expected to be a relic. Astronomers think that all big galaxies have a massive central black hole, but less than 10 percent of these are active today. Active galaxies are thought to be responsible for about 20 percent of all the energy radiated over the life of the Universe, and are thought to have had a strong influence on the way structure evolved in the cosmos. Astronomers, generally, classify AGN into two main types based on the properties of the light they emit, with one type of AGN tending to be brighter. Brightness of the AGN is generally thought to depend on either or both of two factors: the AGN is related to surrounding gas and dust, or to the rate of feeding of the supermassive black hole. Some AGN have been observed to change between these two types over the course of only 10 years as some cycle in brightness, from bright to dim and back. AGN can also be found in dwarf galaxies
It looks like the massive black holes found at the center of the AGN are triggered through galaxy mergers. A merger stirs up gas in both galaxies as infalling gas triggers the black hole on, creating an active galactic nucleus (AGN). The active galactic nuclei (AGN) are the most luminous objects in the universe. They include quasars and blazars. Thick clouds of dust and gas surrounding the black hole can block ultraviolet, optical and low-energy, or soft X-ray, light leaving the hard X-rays only to observe those. Only about one percent of supermassive black holes exhibit this behavior. AGNs are to be found as close to the Earth than under the 650 million light-years mark. At that epoch, a underlying population of fainter quasars thriving in more normal spiral galaxies however represented the most common, and long-term way of turning galactic black holes up into quasars
In a active galaxy, matter falling toward the supermassive black hole powers high-energy emissions so intense that two classes of active galaxies, quasars and blazars, rank as the most luminous objects in the Universe. The inflow of fuel being disrupted towards a galactic black hole makes active galaxies change dramatically of luminosity over the course of a decade only as they part into classes of luminosity. A emission line galaxy is a galaxy undergoing active star formation with its stellar population constantly being refurbished. Due to massive bright blue stars, such galaxies are veiled in a blue tint. Although there are many different types of active galaxy, the different observed properties base on how the galaxy angles into our line of sight. We view the brightest ones nearly face on, but as the angle increases, the surrounding ring of gas and dust absorbs increasing amounts of the black hole's emissions. Such heavily absorbed black hole X-ray emissions are accounting for at least one-fifth of all active galaxies
The energy in a active galaxy probably comes from two sources. The first is probably a ring of star formation surrounding the core. Gravitational disturbance may induce the material around the core to begin collapsing and forming stars at an accelerated rate. The other source is an active galactic nucleus, which is a supermassive black hole surrounded by a disk of matter that is slowly falling into the hole. That disk of matter contains a great deal of gas and dust. The material nearest the black hole is extremely hot. At about between 2 and 4 billions years after the Big Bang, when galaxies usually were forming stars at a rate 10 times the one of today, AGNs with the most powerful, active black holes at their cores produce fewer stars than AGNs with less active black holes. Star formation thus and black hole growth likely increase together up to a point, but the most energetic black holes eventually shutter the star formation. Black holes' accretion of gas likely first provide to the stars' fuel but as they eventually heat up, their radiation disperses the galactic reservoirs of cold gas. Active galaxies may be found as close to Earth than about 14 million light-years

-> More About Blazars
Blazars are the highest-energy type of active galaxy and emit light across the spectrum, from radio to gamma rays. Astronomers think blazars appear so intense because they happen to tip our way, bringing one jet nearly into our line of sight. To be considered a blazar, an active galaxy must show either rapid changes in visible light on timescales as short as a few days, strong optical polarization, or glow brightly at radio wavelengths with a 'flat spectrum', one exhibiting relatively little change in brightness among neighboring frequencies. Astronomers have identified two models in the blazar line. One, known as flat-spectrum radio quasars (FSRQs), show strong emission from an active accretion disk, much higher luminosities, smaller black hole masses and lower particle acceleration in the jets. The other, called BL Lacs, are totally dominated by the jet emission, with the jet particles reaching much higher energy and the accretion disk emission either weak or absent

-> A New Breed of Quasars?
NASA's infrared Spitzer Telescope has recently allowed (the finding has been disclosed in March 2005) to find what might be a new breed of quasars existing at a distance of about 11 billion light-years as they shine like 10 trillions suns. They are enshrouded deep into very dusty galaxies. Galaxies comparable in dustiness -but not in brightness- might exist much nearer Earth

Then comes what might be called the proto-galaxies period. It is a time when the most intense bursts of star birth occurred in massive, bright galaxies as their bursts of star birth took place 12 billion years ago, when the Universe was just under 2 billion years old. Lyman-alpha Blobs (LABs) are gigantic clouds of hydrogen gas that can span hundreds of thousands of light-years and are found at very large cosmic distances. They are featuring the characteristic wavelength of ultraviolet light known as Lyman-alpha radiation. Lyman-alpha radiation is produced when electrons in hydrogen atoms drop from the second-lowest to the lowest energy level. LABs are found in primordial gas clouds surrounding young galaxies. Some of those may be the formation locus of a massive elliptical galaxy that will one day be the heart of a giant galaxy cluster. Those vast cosmic, dim and warm reservoirs of atomic hydrogen glowing with Lyman-alpha emission are seen in the early Universe, which are still visible -- but not the naked eye -- nowadays in our sky. Such gaseous cocoons which envelop earliest galaxies as those are fed by inflows from the intergalactic medium and by outflows from galactic winds. The fact of why they emit Lyman-alpha is still unknown. Proto-galaxies are compact objects which are forming stars at the most important rate of all Universe's history as they grew in size by forming small collections of very hot stars. Such galaxies are grouping into into clusters -or, better, "proto-clusters". Galaxy clusters are the largest objects in the Universe bound together by gravity as it should take several billion years for them to form. Galaxy clusters are enormous collections of hundreds or even thousands of galaxies and vast reservoirs of hot gas embedded in massive clouds of dark matter. In a galaxy clusters, the mass of hot gas is about six times greater than that of all the galaxies combined, and observable brightly in X-rays. Awesome gaseous fountains have been discovered in the centers of galaxy clusters as vast amounts of gas fall toward a supermassive black hole, where a combination of gravitational and electromagnetic forces sprays most of the gas away from the black hole in a cycle lasting tens of millions of years. Radio halos are vast sources of diffuse radio emission usually found around the centres of galaxy clusters. They are thought to form when clusters collide and accelerate fast-moving particles to even higher speeds. Galaxy clusters grow via collisions. A galactic cold front forms when two galaxy clusters merge, as the gas in the core is being sloshed around like liquid in a glass. The cold front moves in a spiral pattern moving outwards as they may be protected from disruption by magnetic fields wrapped around. Magnetic fields play a strong role in shaping spiral galaxies, as they are also compressed by gravitational forces. Mergers between clusters of galaxies should have been more common early in the history of the Universe. The most distant, primitive cluster of galaxies ever found is lying at a distance of 9.6 billion light-years, called CLG J02182-05102, with galaxies mostly old, red and massive ones. Most ancient proto-cluster however, which presumably grew into a modern galaxy cluster, has been seen at 12.6 billion light-years, with buzzing with extreme bursts of star formation in a central galaxy and one enormous, 30 million Sun-mass feeding black hole, both likely the seeds for the cluster which will eventually grow with a giant, central galaxy that will dominate the cluster. A more distant one still has been found by 600 millions years only after the Big Bang at 13.1 billion light-years away, which lies in the reionization epoch (such a observation demonstrates that galaxy clusters participates into the progressive buildup of galaxies in which small objects accrete mass, or merge, to form bigger objects over a smooth and steady process of collision and collection; the five most bright galaxies seen in the cluster are about one-half to one-tenth the size of our Milky Way, yet are comparable in brightness. The galaxies are bright and massive because they are being fed large amounts of gas through mergers with other galaxies. 'Beads on a string, or pockets of gas that condense where new stars are forming are telltale signs of collisions between gas-rich galaxies, a phenomenon known to astronomers as 'wet mergers,' where 'wet' refers to the presence of gas. Dry mergers, by contrast, occur when galaxies with little gas collide and no new stars are formed. Galaxy clusters looks like they are found in deep wells of dark matter that makes up the underlying gravitational scaffolding). At that time of proto-galaxies, generally, galaxy clusters look rare, among isolated galaxies. Galaxy clusters are collections of up to thousands of galaxies bound together by gravity as they were born out of seeds of matter formed in the very early Universe, and grew rapidly by a process called inflation. It might that clusters assembled early are big albeit not very many had time to assemble by then. Energetic "infant galaxies" are gathered around a massive radio pre-galaxy emitting large jets from a supermassive black hole. Our own Milky Way Galaxy appeared at that time. It is 10 billion years old. During this period, previous infrared galaxies have come out of age and though not producing stars anymore they are accounting then for up to two-thirds of stars. One of their mystery is that they did not grow according to the merging model, but only as they had a lot of time to form stars. A thousand extreme galaxies called hot DOGs, or 'dust-obscured galaxies' have been found following NASA's WISE survey in the infrared by the early 2010's. Such extreme galaxies can pour out more than 100 trillion times as much light as our Sun but they are so dusty that they had escaped detection until now. These record setters may have formed their black holes before the bulk of their stars on a other hand and might constitue a new phase of the galaxy formation as they are more than twice as hot as other infrared-bright galaxies with their dust is being heated by an extremely powerful burst of activity from the supermassive black hole. Quasars are continuing to be active and it's even at that time that they are are most numerous (about 3 billion years after the Big Bang). This might mean that galaxies endure several quasar phases due to frequent collisions. On another hand, first galaxies are thought too to be blown out in about less than 2 billion years due to the supernovae explosions of their first generation stars. It might that galaxy clusters begin to build as soon as 3 billion years after the Big Bang as they reach maturity 2 billion years later. Their galaxies then are elliptical, contain red stars, as they are several billion years old already. It's obvious that galaxies' life is mostly determined by the interactions between themselves inside galaxy clusters, and by interaction between themselves and the gas in the clusters. Both events are triggering star formation. Galaxies interact strongly with their surroundings and with each other in those dense interiors of clusters as that can quench their star formation. As gravitation in a cluster is accelerating galaxies inside, that superheats the plasma in between. It might that 'starburst galaxies', producing stars at the high rate of 4,000 a year in short-lived but intense events, instead of 10 for our own Milky Way Galaxy, are seen too during those epochs. Those ultra-luminous, massive, starburst galaxies shining in the infrared are lying more than 8 billion years ago as only a few dozen of these exist in the Universe. They reside in unusually dense regions of space that somehow triggered rapid star formation (indeed, the major mergers between galaxies occur at a later epoch). A explanation to those galaxies might be that gas is raining down on the galaxies, or they are fed by some sort of channel or conduit. They might be the brighter, more distant cousins of the ultra-luminous infrared galaxies (ULIRGS), which are hefty, dust-cocooned, starburst galaxies, seen in the nearby Universe. A starburst galaxy may also be due to interactions inside their galactic, leading to a compression of gas. Massive galaxies resulting from a high star formation rate (in that case, called a 'maximum starburst') have been seen as soon as by 880 million years ago at a time considered the realm of mergers between small galaxies. A starburst galaxy is a galaxy in which unusually high numbers of new stars are forming, springing to life within intensely hot clouds of gas as it also features vast amounts of dust as a result of the frantic star formation. The conditions to produce stars at a high rate might be acquired in a number of ways -- for example by passing very close to another galaxy, colliding into, or as a result of some event that forces lots of gas into a relatively small space. Starburst regions are rich in gas as young stars in these extreme environments often live fast and die young. They also emit huge amounts of intense ultraviolet light, which blasts the electrons off any atoms of hydrogen lurking nearby (a process called ionization), leaving behind often colorful clouds of ionized hydrogen, or HII regions. In a starburst galaxy, dense shock waves are powered by hot, fast galactic winds originating inside the galaxy's star forming regions. Winds push material out of it in such a turbulent way that part of the material can be re-captured by the gravitational pull of the galaxy, gathering into huge turbulent reservoirs of cool, low-density gas, extending more than 30 000 light-years from the galaxy, for example. Those reservoirs consist into cold carbon hydride molecules or CH+. CH+ requires a lot of energy to form with a very short lifetime as it is very reactive as it forms only in small areas where turbulent motions of gas dissipates. By driving turbulence in the reservoirs, these galactic winds extend the starburst phase instead of quenching it. Galactic mergers are also needed to replenish the gaseous reservoirs. One way in which astronomers probe the nature and structure of such galaxies is by observing the behavior of their dust and gas components, in particular, the Lyman-alpha emission which occurs when electrons within a hydrogen atom fall from a higher energy level to a lower one, emitting light as they do so. M81, for example, is a starburst galaxy due to that it has been encountering M82 a few hundred million years ago and gravitational interactions triggered bursts of star formation. M81 is the sky's brightest object in the infrared wavelengths. Faintest of starburst galaxies are blue compact dwarfs. Starburst galaxies contributed significantly to cosmic star formation at 10 billion years from now. One leading theory about how they originated proposes that a collision between two young galaxies could have sparked an intense short-lived phase of star formation. Another theory speculates that, when the Universe was young, individual galaxies had much more gas available to them to feed from, enabling higher rates of star formation. It is likely that growth of supermassive black hole and spurts of star formation may precede the growth of bulges in galaxies, which differs of what is seen from the relatively nearby universe where the growth of galaxy bulges and supermassive black holes appears to occur in parallel. The most fertile bursts of star birth in the early Universe took place in distant galaxies containing lots of cosmic dust. 2013 ESO's ALMA images revealed multiple, smaller galaxies forming stars at somewhat more reasonable rates however. A Wolf-Rayet starburst galaxy holds a large number of the new stars which are of the Wolf-Rayet type – extremely hot and bright stars that begin their lives with dozens of times the mass of the Sun, but lose most of it very quickly via powerful winds

At about two billion years after the Big Bang, a major step in the growth of galaxy and supermassive black hole is that both forming bodies switch off to pushing back the gas and matter which until now was falling. The black holes, that way, are dissipating the heath generated by the infalling process. Such an outflow is lighting up the hydrogen gas still gathered in a 'blob' around the galaxy. That gas, then, is not joining anymore to form more stars, or add to the supermassive black holes as it add to the hot gas found between galaxies -mostly in the frame of galaxy clusters. The re-ionization era, with the quasars ultraviolet light in the active galaxies ionising intergalactic helium, on the other hand, likely had weakened the production of new galaxies during about 400 million years between 11.7 and 11.3 billion years ago. As the existing galaxies collided, on the other hand, that yielded more galactic black holes in their center. At a Universe 3 billion to 4 billion years old, large reddish elliptical-shaped galaxies made up of old stars were numerous. Scientists have wondered whether those galaxies built up slowly over time through the acquisitions of smaller galaxies, or formed more rapidly through powerful collisions between two large galaxies. The massive merger scenario is the really one

When galaxies, during that period, and black holes, are forming at a high rate, black holes can endure powerful outburst. The interaction between the less energetic electrons-producing X-rays from the outburst with the pervasive sea of photons remaining from the Big Bang -the cosmic background radiation- leads to the apparition of cosmic 'ghosts' lurking around the galaxy. The 'ghost' may last for billions of years and measure 2.2 million light-years or so as they may be found too around galaxies with radio emission on large scales which likely track to continued eruptions

Small-sized galaxies of that period, relatively to those of today, have been seen massive and compact at 30 to 40 percent of the galaxies then. Due to such a high gravity, stars, inside such galaxies, are moving fast, at about 1 million mph (or twice the speed of the stars inside the Milky Way Galaxy). The small size and compacity of those early galaxies poses the problem of that, when they merge with other ones, they are growing in size, but not in mass, hence becoming less dense, the mechanism of which is still unknown

-> Galaxies' merger are an obvious actor in the history of the early Universe, 10 to 12 billion years ago. Shells, clouds and arcs of tidal debris in a galaxy are usually the remains of merging events as spirals turn into ellipticals (young elliptical galaxies, in the order of four billion years of age, may show some structure in the form of a bright disk inside the elliptical structure). Such collisions are driving a lot of gas towards the center of the event, triggering both a burst of star formation (1 star is created each day, 100 times the current rate in our Milky Way Galaxy!) and the fusion of the galactic black holes, contributing to the increase of their number in the Universe. The continuing flow of gas keeps triggering more energy, and... a quasar is born! This further, is in line with the observation, at the current epoch, between the mass total of stars in the central bulges and the mass of the central black holes. The quasars thus formed are then cleaning the center of the galaxies' fusion of the infalling gas, through their superwinds, expelling the gas up to tens of thousands of light-years away! A uneven merger of galaxies is called by astronomers a 'minor merger' as the larger one is not disrupted by the merger. Up to half of the matter in our Milky Way galaxy, and in other large galaxies, might come from distant galaxies through a process termed 'intergalactic transfer.' Intergalactic transfer consists into that supernova explosions in a galaxy eject copious amounts of gas out, causing atoms to be transported from one galaxy to another via powerful galactic winds. Such a process occurs over several billion years picture courtesy NASA/CXC/IoA/D.Alexander et al.

->Black Holes and Host Galaxies Really Compete For Life
A study in 2006 found that the interaction between a galaxy and its black hole has as a consequence that when the black hole reaches a critical size relative to its host galaxy, the latter's development comes to a halt, as does the formation of stars in it. This is obviously due to that a large black hole creates unsuitable environment for stellar birth, either that the black hole powerfuls jets blows away the gas and matter stars would feed upon, or that the gas in the galaxy is stirred down towards the black hole, hence heated and inappropriate to stars formation

->About the Large Magellanic Cloud
Both the Large and the Small Magellanic Clouds (LMC, SMC) are satellites to our Milky Way Galaxy. As far as the LMC is concerned, astronomers believe that approximately six billion years ago, not long before our solar system formed, this dwarf galaxy was shaken up via a close encounter with the Milky Way. The resulting chaos triggered bursts of massive star formation similar to what is thought to occur in more primitive galaxies billions of light-years away

->Ultradense Baby Galaxies Numerous at that Epoch of the Universe
Strong-weighted baby galaxies have been pinpointed at distances of 11 billion years, with a size of about 5,000 light-years and a mass of 200 billion Sun, that is about the weigh of a current spiral galaxy! Those ultradense galaxies might be due to interaction in their formation with dark matter, as they might represent up to the half of all the galaxies of such a mass at that epoch of the Universe and might be a kind of standard them, as other galaxies would have been more massive. 'Compact elliptical galaxies' are galaxies whose star formation was finished when the universe was only 3 billion years old. After a swift burst of star formation during 40 millions years, they eventually merged with smaller galaxies to form giant ellipticals. The stars in such galaxies were packed 10 to 100 times more densely than in today ellipticals. It might that the progenitors to compact ellipticals have been the 'submillimeter,' dusty galaxies of that time

A bulge is thought to play a key role in how galaxies evolve, and to influence the growth of the supermassive black holes. Most galactic bulges may be complex composite structures rather than simple ones, with a mix of spherical, disk-like, or boxy components. In some dwarf galaxies, their black hole is not found at their center, and wandering suggesting galactic mergers which knocked off the black hole off center. That could participate, generally, into the theory of how black holes formed. At that epoch, the rate of star formation in young galaxies is closely related to their total mass in stars and it was then the 'Golden Age' of galaxy formation, approximately 10 billion years ago. The stellar mass of a galaxy is the best predictor of star formation rate in that high redshift Universe, where high-mass galaxies were the norm. Also, rapidly rising gas content occurred at the time in galaxies. Aged massive, 10 billion-year old galaxies recently were found infused with fresh gas, triggering a massive star formation along their external border as the origin of that gas is still ill-explained. Galaxy clusters seen at 10 billion years in the past, are seen to have their galaxies produce stars at a higher rate when close to the center of the cluster than at the edges, which is the opposite of how things work nowadays, where cores of galaxy clusters are known to be galactic graveyards. Such galaxies, which are large in size, on the other hand, might well be the missing link between the active galaxies and the quiescent ones of the later Universe. 70 massive, young galaxies in the constellation of Ursa Major are the most extreme galaxies in the Universe at the peak of their activity, some 11 billion light-years from there, with a astonishing scale of star formation. Galaxies of the time usually are full of turbulences because their gravity attracts vast, external gas clouds. As the gas clouds enter a galaxy, they fall into haphazard orbits which cause turbulence in the host galaxy, which can drive star formation. The famed Sombrero Galaxy is a round elliptical galaxy with a thin disk embedded inside and one of the first known galaxy to exhibit characteristics of the two different types of galaxy, either ellipticals or spirals. Observations in 2012 have shown that the Sombrero is not simply a regular flat disk galaxy of stars as previously believed, but a more round elliptical galaxy with a flat disk tucked inside. In visible views, the galaxy appears to be immersed in a glowing halo, which scientists had thought was relatively light and small. The Spitzer space telescope in the infrared has seen old stars through the dust and reveals the halo has the right size and mass to be a giant elliptical galaxy. One scenario proposed is that a giant elliptical galaxy was inundated with gas more than nine billion years ago. Early in the history of our Universe, networks of gas clouds were common, and they sometimes fed growing galaxies, causing them to bulk up. The gas there spun out into a flat disk. Such elliptical galaxies with a disk inside -with a other example the Centaurus A galaxy- might represent varied stages of a evolution, Centaurus a earlier stage of evolution than the Sombrero. That also explains why such galaxies have a high number of globular clusters around them, which is typical of elliptical galaxies. By late 2012, a new galaxy class has been identified as nicknamed 'green bean galaxies' as their supermassive black hole is having the entire galaxy glowing bright green due to ionized oxygen. They are amongst the rarest objects, and about 16 only, in the Universe. They are larger than so-called 'green pea galaxies' which are very small, luminous galaxies undergoing vigorous star formation. The black hole in green bean galaxies is much less active than expected from the size and brightness of the glowing region which might hints to that the glowing regions must be an echo from when the central black hole was much more active in the past, and that they are now gradually dimming. Green bean galaxies likely are a very fleeting phase in a galaxy’s life and show a light echo, shutdown processes of early galactic black holes

During the peak epoch of galaxy formation, 10 billion years ago, galaxies were dominated by baryonic or 'normal' matter, in a stark contrast to now where the effects of dark matter seem to be much greater. Dark matter was less influential in the early Universe as normal matter typically nowadays accounts for about half of the total mass of all galaxies on average. This explanation is consistent with observations showing that early galaxies were much more gas-rich and compact than today’s galaxies with a same decreasing velocity trend away from the centers of those ancient galaxies. And also with that galaxies of the time had already efficiently condensed into flat, rotating discs, while dark matter halos surrounding them much larger and more spread out

Usual Galaxies. Starting at 4.5 Billion Years After the Big Bang

->A Renewed View of The Galactic Universe!
A surplus of infrared light has been recently found by late 2014 filling the spaces between galaxies, a diffuse cosmic glow as bright as all known galaxies combined. The glow is thought to be from orphaned stars flung out of galaxies. The discovery might redefine galaxies, which may not have a set boundary of stars, but instead stretch out to great distances, forming a vast, interconnected sea of stars. That is true despite numerous collisions between galaxies

->Galactic Supermassive Black Holes the Results of Mergers!
It appears now that the supermassive black holes found at the center of most galaxies do not grow by themselves nor appear big all a sudden. Such galactic black holes are the result of galaxies' mergers. As galaxies are enduring several merges in their lifetime, their respective black holes merge together too, leading to the construction of the supermassive variety. Such merging galaxies are so much enshrouded in dust that it takes hundreds of million to 1 billion of years after the fusion, for the astronomers to be able to have a look at the center of such galaxies! Even supermassive black holes merge between themselves to a single immense black hole. Galactic black hole mergers is strongest for gas-rich hosts with obscured luminous black holes

Then comes a usual evolution of sort. More irregular galaxies than today are found (as they currently account for one quarter of all galaxies). Such galaxies were not always like they are today and have once fallen into one of the regular classes of the Hubble sequence, as some might result from a galactic collisional event. There are two types of irregular galaxy. Type I are usually single galaxies of peculiar appearance containing a large fraction of young stars, and showing luminous nebulae as Type II irregulars include the group known as interacting or disrupting galaxies due to two or more galaxies colliding, merging or otherwise interacting gravitationally). 'Ultra-diffuse galaxies' are galaxies devoided of stars, or even a central massive black hole, and looking like see-throug ones. That type of galaxies look like being surprisingly common. Galaxies appears to be a lot more numerous than today -between 3 and 10 times more. In most spiral galaxies, the innermost portion forms first and contains the oldest stars. As the galaxy grows, its outer, newer regions have the youngest stars. About 20 percent of matter in a galaxy is found in their halo. A galactic halo contains both dark and ordinary—or baryonic—matter that is primarily in the form of a hot ionised gas. Halo gas fuels star formation as it falls towards the centre of the galaxy, while other processes, such as supernova explosions, can eject material into the galactic halo. Such ejection processes can shut down star formation. Small satellite galaxies also accounts for material flow downward. Galaxies underwent a big change in the mass of their stars over the past 10 billion years, bulking up by a factor of 10 as most of that stellar-mass growth happened within the first 5 billion years of their birth, and that the peak of star formation around 10 billion years ago. Galaxies formed along the gas filaments of the web Universe, as some voids existed -- and still exist -- there. In our vicinity, the 'Local Void' is a region of the Universe sparsely populated with galaxies. The Local Void is roughly 150 million light-years across. Galaxies there did -- do -- not feature much star formation as they may be gravitationally attracted to more populated regions later where star formation is triggered by gas raining down, or a dense gas filament. Star formation, on a other hand, may slow down when a galaxy becomes a satellite to a much larger one. When the galaxies slow down making stars, their growth by merger or accretion decreases as well. Vertical distribution of stars relative to a galaxy's plane suggests that heating of the disc plays an important role in producing the stars seen away from the plane of the galaxy. Galaxies are becoming mature and sort into present categories: spirals, ellipticals, irregulars. Galactic coronas, generally, are huge, invisible regions of hot gas that surrounding a galaxy, forming a spheroidal shape. Ellipticals are yellow-white in color as spirals bluish. Irregular dwarf galaxies are actually one of the most common types of galaxy in the Universe. A diffused and disorganized appearance is characteristic of a irregular dwarf galaxy. Lacking a distinctive structure or shape, they are often chaotic in appearance, with neither a nuclear bulge nor any trace of spiral arms. Astronomers suspect that some irregular dwarf galaxies were once spiral or elliptical galaxies, but were later deformed by the gravitational pull of nearby objects, or mergers with other galaxies. Irregulars are thought to be similar to the first galaxies that formed in the Universe. Only very little of the irregulars' original gas has been turned into stars. Astronomers thought spiral galaxies had settled into their present form by about 8 billion years ago, with little additional development since. The largest galaxy observed in the Universe is NGC 262, at 1.3 million light-years in diameter, followed by NGC 6872 at 500,000 light-years across. Free hydrogen is the basis material for new stars to form inside a galaxy. Dust-rich galaxies are typically spiral or irregular, whereas the dust-poor ones are usually elliptical. Galaxies in fact, as studied in 2012, were steadily changing over this time period. Disorganized motions in multiple directions occur as a steady shift towards greater organization to the present time however makes the disorganized motions dissipate and rotation speeds increase and let place to the current, stabilized galaxies. The smaller the galaxies, the highest level of disorder. Disk galaxies like our own Milky Way unexpectedly reached their current state long after much of the Universe's star formation had ceased. Over the past 8 billion years, the galaxies lose chaotic motions and spin faster as they develop into settled disk galaxies. NGC 6872 barred spiral galaxy is currently the largest galaxy as it spans more than 522,000 light-years and is located by some 212 million light-years from Earth in southern constellation Pavo, the Peacok. Its size likely have resulted from gravitational interactions with two other galaxies, of both one a dwarf! In the past 8 billion years, the number of mergers between galaxies large and small has decreased sharply and the overall rate of star formation and disruptions of supernova explosions associated with star formation. Gravitational interactions between galaxies go from glancing blows to head-on collisions, tidal influencing, mergers, and galactic cannibalism and even a close passage between two galaxies can trigger a flurry of star formation inside, or even quasars and supernovae. The majority of these interactions at larger galaxies like, for example, our Milky Way Galaxy, involves significantly smaller, dwarf galaxies. Those coalescing events scramble the winding structures of the original galaxies, smoothing and rounding their shape. A galaxy collision propels much of the galaxy material toward the central black holes. The formation of high-mass X-ray binaries is a natural consequence of blossoming star birth following a galaxy merger. Some of the young massive stars often form in pairs and evolve into these systems. When the relative speed of two galaxies colliding is too fast, they do not merge as their small separation have them distorting one another through the force of gravity, changing their structures on a large scale. During a galaxy merger, it is the larger galaxy's central black hole which turns active, voraciously gobbling gas and dust. 'Flocculent galaxies' are galaxies which lack the clearly defined, arcing structure to their arms that shows up in usual spirals, which are called 'grand design spirals.' In flocculent spirals, fluffy patches of stars and dust show up here and there throughout their disks as they are patchy and discontinuous giving a galaxy a fluffy appearance. Sometimes the tufts of stars are arranged in a generally spiraling form, as illuminated star-filled regions can also appear as short or discontinuous spiral arms. About 30 percent of galaxies are flocculent galaxies as only approximately 10 percent are of the grand design spiral-type. A 'galaxy aggregate' is, as the name suggests, a central galaxy surrounded by a handful of luminous knots of material -- the locus of star formation -- that seem to stem from it, extending and tearing away and adding to or altering its overall structure. A galaxy aggregate is also experiencing an extremely high rate of star formation, possibly triggered by an earlier interaction with another galaxy. Only a few percent of galaxies in the nearby universe are merging, but galaxy mergers were more common between 6 billion and 10 billion years ago. Mergers between galaxies keeps occurring by the present age however, like as recent as by 130 million years ago. Merging galaxies can produce jets of charged particles that travel at relativistic speeds. During a merger, the fall of gas and dust towards the center of a galaxy and triggering a burst of star formation can also create a unstable environment. Shockwaves or powerful winds produced by the growing black hole can sweep through the galaxy, ejecting large quantities of gas and shutting down star formation. The relationship between mergers, bursts of star formation, and black hole activity is complex, and scientists are still working to understand it fully. In mergers, the original galaxies are often stretched and pulled apart as they wrap around a common center of gravity. After a few back-and-forths, this starry tempest settles down into a new, round object usually technically known as a elliptical galaxy. Those stars do not last long, and after a few billion years the reddish hues of aging, smaller stars dominate an elliptical galaxy's spectrum. A merging of galaxies can trigger black holes to start feeding, an important step in the evolution of galaxies. Black holes during a galactic merger, might flicker rather than radiate with a more or less constant brightness throughout the process. In the recent times of the history of galaxies, the outcome of a galactic merger looks like it may be a disc galaxy -like a spiral or a lenticular- as well as a elliptical, which might likely explain a majority of spiral galaxies in our Universe. Interactions between galaxies can range from minor interactions involving a satellite galaxy being caught by a spiral arm, to major galactic crashes. Galaxy mergers are triggering enormous shock waves -similar to sonic booms- inside a galaxy cluster. One of the colliding galaxies, when a disc galaxy, keep its rotation for a while. The driving force of the evolution of galaxies, generally, are O-type, very bright high-mass stars. All of them except irregulars are surrounded by a dark matter halo and vast clouds of gas. In a hemisphere of the Universe more spiral galaxies are rotating clockwise, while in the other hemisphere more are counterclockwise. Spirals form by mergers of proto-galaxies and star clusters. They already come importantly under their barred form. In terms of spiral galaxies, astronomers term 'the winding problem' the fact that arms should become wound tighter and tighter as time passes but this is not what we see. In spirals, stars on the inside orbit the galaxy faster than those further out. Galaxies are classified into different types according to their structure and appearance. This classification system is known as the Hubble Sequence, named after its creator Edwin Hubble. Spiral galaxies are ubiquitous across the cosmos, comprising over 70 percent of all observed galaxies. Grand design spiral galaxies represent one-tenth of spirals and are in many ways the archetype of a spiral galaxy. They are characterized by their prominent, well-defined arms, which circle outward from a clear core. Barred spiral galaxies, or SB account for approximately two thirds of all spirals (a bar of stars is common throughout the Universe and found within the majority of spiral, many irregular, and some lenticular galaxies. Even the Large and Small Magellanic Clouds, are barred). Galaxies of this type appear to have a bar of stars slicing through the bulge of stars at their center. Bars are a natural product of cosmic evolution, and part of the galaxies' endoskeleton. Bars are a sign of galactic maturity as they are also thought to act as stellar nurseries. A bar is thought to invigorate the galaxy's central region somewhat, sparking activity, corralling and funneling inward material and fuel needed. Over time, as the fuel runs out, the central regions of a galaxy become quiescent and star-formation activity shifts to the outskirts, possibly leading a outer ring due to spiral density waves and resonances induced by the central bar helping convert trapped gas to stars. The SB classification is further sub-divided by the appearance of a galaxy's pinwheeling spiral arms; SBa types have more tightly wound arms, whereas SBc types have looser ones. SBb types lie in between. The very existence of spiral arms was for a long time a mystery as they should become wound up ever more tightly, causing them to eventually disappear after a cosmologically short amount of time. It was only in the 1960s that astronomers found that, rather than behaving like rigid structures, spiral arms are in fact areas of greater density in a galaxy's disk, with gas and dust moving through density waves, becoming compressed and lingering before moving out of them again. In barred spirals, the small bar of dust and gas is helping to fuel the new stars. Rings can form around a spiral galaxy in particular locations known as resonances, where gravitational effects throughout a galaxy cause gas to pile up and accumulate in certain positions. These can be caused by the presence of a bar within the galaxy, or by interactions with other nearby objects. Some galaxies essentially act as giant astronomical lasers that also spews out light at microwave wavelengths, as they are termed 'megamaser' ('maser' being the term for a microwave laser). Such megamasers such as the UGC 6093 galaxy, for example, can be some 100 million times brighter than masers found in galaxies like the Milky Way galaxy. Ellipticals form by mergers of spirals (forming in high or low-density clusters, this is surely occurring based on low-velocity mergers) as a oval of stars is typical of such ellipticals. 'cD galaxies' look similar to elliptical galaxies but they are bigger and have extended, faint envelopes as they grow at the center of a galaxy cluster by swallowing smaller galaxies drawn there by gravity. A star-depleted core, generally, distinguishes massive galaxies from standard elliptical galaxies, which are much brighter in their centers which is likely due to supermassive black hole pushing stars away. Every tenth elliptical is a shell galaxy where the stars in its halo are arranged in layers, in a onion-like structure. Such structures are thought to develop as a consequence of galactic cannibalism, yielding first oscillating centers about a common center, which ripple outwards forming the shells of stars. Shells of such a galaxy usually are skewed somewhat. Universe’s largest elliptical galaxies continue making stars long after their peak years of star birth, with knots of hot, blue stars forming along the jets of active black holes found in the centers of such giants. High-energy jets shooting from the black hole heat a halo of surrounding gas, controlling the rate at which the gas cools and falls into the galaxy highlighting once more the regulating action of stars birth and black holes in galaxies. Before old age sets in, some freshly formed elliptical galaxies experience a final flush of youth, as galaxies smashing together pool their available gas and dust, triggering new rounds of star birth. Dwarf galaxies are the most common galaxies in the Universe now as how relatively isolated, low-mass systems such that, which are lacking of large amounts of gas, sustain star formation for extended periods of time remains a mystery. Small galaxies, generally, have lower gravitational potentials allowing to less energy to move matter inside that in other galaxies and making them far more likely to be filled with streams and outflows of speedy charged particles known as galactic winds (due to new-born stars). Dwarf galaxies are thought to form from the material left over from the messy formation of their larger cosmic relatives, as they featured gravitational interactions with galaxies nearby, sparking stars formation. Super-thin galaxies are spiral galaxies where its diameter is at least ten times larger than the thickness as they have a low brightness and almost all of them have no bulge at all nor dust lane. In a sample of approximately 800,000 galaxies no more than 3.5 billion light-years from Earth, 53 of the brightest galaxies intriguingly had a spiral, rather than elliptical, shape (the most common one in the Universe) and are considered 'super spirals'. Super spirals can shine with anywhere from eight to 14 times the brightness of our Milky Way, at as much as 10 times its mass, and twice to even four times its width. Super spirals also give off copious ultraviolet and mid-infrared light, signifying a breakneck pace of churning out new stars, as high as 30 times that of our Milky Way Galaxy. Super spiral buck the process of quenching which makes ordinary spirals have star formation prevented due to too much captured gas. Because some super spirals contain two galactic nuclei, a sign of a galactic merger, super spirals might follow the merger instead of a elliptical, having the pooled gases settle down presto into a new, larger stellar disk. Super spirals could fundamentally change our understanding of the formation and evolution of the most massive galaxies. Deep-field surveys had pinpointed the merger rate of galaxies over the last 8 to 9 billion years to anywhere from 5 percent to 25 percent of the galaxies were merging. Recents finds are that large galaxies merged with each other on average once over the past 9 billion years a small galaxies were coalescing with large galaxies more frequently, or three times more. Mergers are of importance into the evolution of the Universe as galactic collisions may be a key process that drives galaxy assembly, rapid star formation at early times, and the accretion of gas onto central supermassive black holes at the centers of galaxies. In case of a collision, gas may not move inwards into the galactic black hole of one of both galaxies, triggering star formation in the process but it may heat up when colliding with existing galactic gas and, above all, steer such gas which is cool as that cooling temperature expanding quenches star formation instead. Our own Milky Way galaxy had several such mergers with small, dwarf galaxies in its recent past, which helped to build up the outer regions of its halo. Sound waves from the very early Universe left imprints in the patterns of galaxies, causing pairs of galaxies to be separated by approximately 500 million light-years. When interacting galaxies actually pass through one another, with the smaller one diving deep but off-center into, that may result into a large, outer arm appearing partially like a ring. That is due to the inner set of spiral arms being highly warped out of the plane and with varied positions relative to the bulge. Collisions more generally cause tidal tails, which are thin, elongated streams of gas, dust and stars that extend away from interacting galaxies. Material is sheared from the outer edges of each body and flung out into space in opposite directions, forming two tails. They almost always appear curved. Stellar streams are also hallmarks of galactic interactions. "Ring galaxies," as far as they are concerned are thought to form when one galaxy slices through the disk of another, larger, one. Such rings may be composed of black holes or neutron stars in binary systems, which often are ULXs -- ultra luminous X-ray sources -- as the ring, generally is triggerd by ripples yielding a expanding ring of gas among which star formation occurs. A disruption of that type redistributes the material into a dense central core, encircled by bright stars in a ring where star formation is intense, both structures marking the galaxies which collided. The ring marks the limit of a shock wave. Some starburst rings can also be caused simply by the galaxy's oval shape. Ultraluminous X-ray, or ULX sources are believed to be one per galaxy as most galaxies however don't have any; they are still ill-explained as they are sources of X-rays and known for their strong luminosity exceeding that on neutron stars or stellar black holes. Low surface brightness (LSB) galaxies, the existence of which was first proposed in 1976 was confirmed in 1986, are more diffusely distributed galaxies than usual. With surface brightnesses up to 250 times fainter than the night sky, these galaxies can be incredibly difficult to detect as most of the matter present in LSB galaxies is in the form of hydrogen gas, rather than stars and their centers do not contain large numbers of stars. Astronomers suspect that this is because LSB galaxies are mainly found in regions devoid of other galaxies, and have therefore experienced fewer galactic interactions and mergers capable of triggering high rates of star formation. LSB galaxies instead appear to be dominated by dark matter. Classical galactic bulges, generally, the bright, dense, elliptical centers of galaxies are relatively disordered, with stars orbiting the galactic center in all directions. In contrast, in galaxies with so-called pseudobulges, or disc-type bulges, the movement of the spiral arms is preserved right to the center of the galaxy. A blue compact dwarf (BCD) galaxy is a galaxy about a tenth of the size of a typical spiral galaxy and made up of large clusters of hot, massive stars that ionize the surrounding gas with their intense radiation, glowing brightly with a blue hue, giving galaxies their characteristic blue tint. BCDs are composed of many large clusters of stars bound together by gravity and they contain relatively little dust and few elements heavier than helium. BCDs don’t contain either a lot of dust, or the heavy elements, making their composition very similar to that of the material from which the first stars formed in the early Universe. Stars in those BCDs will burn through their supplies of gaz in only millions of years). "Starburst" galaxies have a a significant fraction of their energy output not coming from normal populations of stars but from the extraordinarily high amount of star formation occurring in their nucleus, that activity might be too in a link with a supermassive black hole here. As, by 7 billion years old, galactic black holes triggered geysers of gas shooting into space at up to 2 million miles an hour, which shut down star birth by blowing out any remaining fuel, stars are thought to be also turning out the lights on their own formation epoch with their own outflows of gaseous fuel in their galaxy when their starburst compact enough. Should a flux of forming stars cold gas stops, a galaxy rapidly evolves and may eventually become a red, dead elliptical galaxy. These extreme starbursts are quite rare, however, so they may not grow into the typical giant elliptical galaxies seen in our nearby galactic neighborhood. They are, instead, more compact. A 'Liner-type Active Galactic Nucleus,' on a other hand, is a highly energetic central region in a galaxy. LINER stands for 'low-ionization nuclear emission-line region,' a the nucleus emits emission from weakly-ionized or neutral atoms of certain elements. Around one third of all nearby galaxies are thought to be LINER galaxies. Many LINER galaxies also contain intense regions of star formation. This is thought to be intrinsically linked to their centers as it is still unknown whether the starbursts pour fuel inwards to fuel the LINERs, or this active central region triggers the starbursts. A vast halo of hot gas may be found around regular spiral galaxies as chimneys cleared in the galactic mass by supernovae explosions is driving that from the disc and the gas returning to the disc, like a 'galactic fountain of youth.' Filaments of dust and gas escaping the plane of a galaxy into the halo may also reveal that material is ejected due to supernovae or intense stellar formation activity. Powerful stellar winds can blow dust and gas over hundreds of light-years in space. Complex accretion and 'feedback' processes by which galaxies acquire gas and then later expel it after chemical processing by stars regulate the life of galaxies over billions of years. Some galactic central regions are known like a HII nucleus, with the presence of ionized hydrogen, places likely to be creating many new stars. Galaxies continuously recycle immense volumes of hydrogen gas and heavy elements. In a galaxy, the interstellar medium generally runs from the cool molecular gas in star-formation gas clouds to the hot gas that is driven into when massive stars die in supernova explosions. This process allows galaxies to build successive generations of stars. This ongoing recycling keeps some galaxies from emptying their "fuel tanks" and stretches their star-forming epoch to over 10 billion years. Galactic rain, generally, in the form of cool gas clouds which mist a galaxy cluster and its interaction with black holes is a factor of star formation in the cluster. A balance is found between material falling into the black holes and material left to star formation. In a typical galaxy, like the Milky Way, only a fraction of the total gas supply is actively forming stars, with the bulk of the fuel lying dormant as star-forming regions are randomly distributed throughout the galaxy. Powerful stellars winds are pushing some galactic gas into the intergalactic medium. Star formation however is slowing, with our Milky Way Galaxy, for example producing nowadays about one solar-mass worth of new stars per year only. Star-forming galaxies, generally are swallowing mass from the intergalactic medium to add to forming stars. Astronomers believe that the color and shape of a galaxy is largely controlled by gas flowing through an extended halo around it. A large mass of clouds is falling through the giant halo, fueling star formation. Some of this gas is recycled material that is continually being replenished by star formation and the explosive energy of novae and supernovae, which kicks chemically enriched gas back into the halo. Halos usually are absent from galaxies that have stopped forming stars. In these galaxies, the recycling process eventually leads to ignite a rapid firestorm of star birth which can blow away the remaining fuel, essentially turning off further star-birth activity. Those galaxies can drive two-million-degree gas very far out into intergalactic space at speeds of up to two million miles per hour. That's fast enough for the gas to escape forever and never refuel the parent galaxy. Gas-rich star-forming spiral galaxies thus can evolve to elliptical galaxies that no longer have star formation. Clusters continue to form. A mature galaxy cluster holds both evolved stellar populations in the member galaxies and a hot, metal-rich gas composing the intracluster medium. At 3 billion light-years from us, Abell 1758 is a object where four galaxy clusters are merging together. Around half of the galaxies we know of in the Universe, on the other hand, belong to some kind of group akin to our Local Group. Galaxy clusters, generally, are gigantic assemblies of galaxies permeated by super-heated gas that shines brightly in X-rays. Galaxy clusters may endure mergers between themselves. The space permeating between the constituent galaxies of galaxy cluster, or the 'intracluster medium' (ICM) features high temperatures, created by smaller structures forming within the cluster. This results in the ICM being made up of plasma, which is ordinary matter in a superheated state. The ICM is very luminous in X-rays. Galaxies moving in a cluster, generally, endure ram-pressure stripping, as gas is removed

The 'web Universe' finally is made of the whole of galaxy clusters and lone galaxies, which formed along the filaments of primitive gas picture site 'Amateur Astronomy'

The majority of the mass in a galaxy cluster exists in the form of non-luminous dark matter. Some galaxy clusters are largely composed of hot gas, and mostly bright in the X-ray wavelength domain and thus termed 'X-ray galaxy clusters.' Diffuse light around the brightest galaxies in a cluster comes from intergalactic stars strung out between the constituent galaxies of the cluster, as the origins of such stars is still badly know. One theory is that they may have been stripped from their host galaxies during mergers and interactions. Collisions between clusters of galaxies yield a pattern of cold fronts inside a some may last billions of years albeit passing through a harsh environment of sound waves and turbulence caused by outbursts from the supermassive black hole at the center of a cluster. That might be due to they are wrapped into a magnetic fields acting like a barrage. Giant sound waves about twice the width of the Milky Way Galaxy may also be found among a galaxy cluster. A galaxy cluster may host a giant radio halo, powerful shockwaves. All galaxy clusters are filled with hot gas threaded with magnetic fields. 'Jellyfish galaxies' feature tentacles which are produced by a process called ram pressure stripping: galaxies fall at great speed into galaxy clusters due to their mutual gravitational attraction and there they meet a hot, dense gas which forces tails of gas out of a galaxy and triggers starbursts within the galaxy. That process likely makes it possible for the gas to reach the central regions of the galaxies, feeding their luminous black hole. For a galaxy, belonging to a massive galaxy cluster brings effects, mostly bursts of star formation due to gravitational interactions between galaxies in the cluster. 'Massive galaxy clusters' typically have a mass of about one million billion times the mass of the Sun! Galaxy clusters are less numerous and less tight than today's but they emit more X-rays. The outer reaches of galaxy clusters show similarity in their X-ray emission profiles and sizes. More massive clusters are simply scaled up versions of less massive ones. A 'field galaxy' is a rather isolated one instead of being inserted into a galaxy cluster. Galaxy clusters nowadays comprise tens, hundreds or even thousands of galaxies as the central galaxy in a cluster contains a supermassive black hole roughly a thousand times more massive than the one at the center of our own Milky Way Galaxy. Gas held at the center of a galaxy cluster is interacting with bubbles of gas expelled by the core galaxy's active supermassive black hole as glowing filaments extending from the galaxy trace bubbles of gas blown violently outward by the black hole. Large filaments are connecting galaxies inside a galaxy cluster. Galaxies with hidden supermassive black holes tend to clump together in space more than the galaxies with exposed, or unobscured, black holes, because of larger halos around the first ones, pulling galaxies toward it, causing them to clump. Astronomers do not know why the hidden black holes would have larger halos of dark matter. All spiral and elliptical galaxies feature dark matter which acts like the scaffolding holding a galaxy's components together. Dark matter in a galaxy, generally, slow the motion of stars and globular clusters at the outskirt of it. The ratio of dark matter to normal matter in a galaxy, generally, changes with time, as dark matter gets more important than the normal one. Galaxy clusters contain a vast reservoir of hot gas, larger than all of the galaxies in a cluster combined. Such a hot gas should cool over time and sink to the main, old galaxy at the center of the cluster, forming huge numbers of stars. However, most galaxy clusters have formed very few stars during the last few billion years as the supermassive black hole in the central galaxy of a cluster pumps energy into the system through powerful sound waves and jets, preventing cooling of gas from causing a burst of star formation. Some large clusters however, like the Phoenix cluster, one of the largest objects in the Universe, do not feature the case and allow for large star formation. Such a exception however usually do not last long. Galaxies at the center of most clusters, generally, may have been dormant for billions of years. Clusters usually are centered around one old, monstrous galaxy containing a massive black hole. Brightest Cluster Galaxies (BCGs — the brightest galaxies within their host clusters) are among the most massive and luminous galaxies in the Universe. They are generally huge elliptical galaxies and are likely to host active galactic nuclei in their cores. BCGs might being fueled by cold gas from their home galaxy as star formation in older BCGs no longer significantly contributes to the galaxy’s growth; instead, the stellar growth then occurs through mergers. The largest known galaxy cluster is the El Gordo Cluster, catalogued as ACT-CL J0102-4915, as located by 9.7 billion years from Earth and 3 million billion times the mass of our Sun. Dark energy tugs the clusters apart and slows down the process generally. Clusters are forming by many sub-clusters mergers. During collisions between galaxy clusters, a process known like 'sloshing,' similar to wine sloshing in a glass that was jerked sideways, had the smaller of both slosking back and forth relative to the larger's center. When the collision is off-center, that ends up in a spiral pattern. The supermassive black hole of the giant elliptical galaxy located at the center of the larger of the clusters also participates as it evacuates bubbles of materials. Both activities, sloshing and that of the black hole's helps prevent cooling of the gas in the main cluster's core. That additionally sets limits on the growth of the giant elliptical galaxy and black hole. Young clusters are embedded into vast gas clouds emitting in X-rays. Hence their member galaxies are growing fast. Inside those clusters, galaxies are colliding, gaining or losing dark matter, and forming stars due to the pressure of the cluster's gas against their own gas. Collisional possibilities inside more usual galaxy clusters eventually is loosening material from collided galaxies which eventually is dispersed through the cluster center, fueling stars and star clusters outside any galaxies. In such a context stars are going supernovae in about 10 million years. In case of a collision between two galaxies of a different size, the starburst activity typically begins in the minor galaxies earlier than in the major galaxies. These effects could be because the smaller galaxies have consumed less of the gas present in their nuclei, from which new stars are born. Galaxy clusters are millions of light-years across, and most of their normal matter comes not so much in terms of galaxies but in the form of hot X-ray-emitting gas that fills the space between the galaxies. The ratios, in a cluster, of the varied forms of matter -normal or dark matter, dark energy- composing the Universe are akin to what is found elsewhere. In the central regions, gas is repeatedly whipped up and smoothed out by passing galaxies as, at a cluster's borders, fresh infalling gas tends to form irregular clumps and enter there. Most galaxies in the Universe now reside in groups and clusters as galaxy clusters are the largest structures in the Universe, comprising hundreds to thousands of galaxies bound together by gravity. Galaxy clusters contain hundreds or thousands of individual galaxies that are immersed in gas with temperatures of millions of degrees. Dark matter also participates. When two galaxy clusters smash into one another, their dark matter and gas separate as their compact cores of gaz do no exist anymore. Over time, the gas in the centers of galaxy clusters should cool enough that stars form at prodigious rates, which is not the case. That should be due to energy radiated out from cavities carved into the infalling gas from jets from supermassive black holes in large galaxies in the middle of the clusters. Galaxies can be gravitationally ripped apart inside clusters, releasing stars loose, when they plunge through the center of a cluster where gravitational tidal forces are strongest. The special environment of galaxy clusters generally, including the effects of frequent collisions with other clusters or groups of galaxies and the presence of large amounts of hot, intergalactic gas, is likely to play an important role in the evolution of their member galaxies. However, it is still unclear whether cluster mergers trigger star formation, suppress it, or have little immediate effect. Shock waves, which are like sonic booms, form during the collision, for example, leading to the collapse of clouds of gas and the formation of star clusters. Galaxy clusters are separated from other clusters by 100 million light-years on average as clusters with closely packed galaxies, that density is lesser than for sparser clusters. Galaxy clusters eventually merge themselves into superclusters. A filament containing hundreds of galaxies, spanning 8 million light years has been observing connecting two or three clusters of galaxies which are in the process of becoming a supercluster together as intense star formation occurs in that filament as galaxies there are crushed by gravity. Such a filament likely also plays the role of funneling its galaxies down to the core of the supercluster where they will eventually turn large, red and old ellipticals over billions of years. Galaxy superclusters are full of red and dead elliptical galaxies which contain aged and reddish stars only. Surprisingly large amounts of cold gas might be extant in giant ellipticals outside those located at the center of a cluster. Such galaxies however do not yield stars, which might be linked to the important role that supermassive black holes play in the evolution of their host galaxies. Black holes' outburst dump most of their energy into the center of the galaxy, where the cold gas is located, preventing the cold gas from cooling sufficiently to form stars. Black holes further, in some elliptical, which emit jets has those preventing the gas around to sufficiently cool too. Star and galaxies formation is continuing until 7 billion years have elapsed since the Big Bang. A study of the star formation inside dwarf galaxies is throwing some light unto how that works and could maybe be extended to the process inside larger galaxies. Pockets of intense star formation propagate throughout the galaxy, like a string of firecrackers going off with the total duration of all the starburst events reaching about 200 million to 400 million years due to explosions of the first stars to form and then turn supernovae triggering perturbation in the neighbouring areas. Instead of forming eight stars every thousand years, the galaxies are seen making 40 stars every 1,000 years. A starburst episode, or some intense star formation, in a galaxy, generally, produces a excess of ultraviolet emissions and possibly triggered by galactic collisions. The formation of stars may also occur when a galaxy is infalling into a galaxy cluster, like the case for the IC 3418 galaxy, which is plunging into the entire Virgo cluster of 1,500 galaxies 54 million light-years away from Earth, at a speed of 2 million miles per hour (3.2 million km/h). A tail of gas is thus produced where a crucial ingredient for star formation - dense, heavier clouds of gas called molecular hydrogen - formed in the wake. Strong turbulence promotes cloud formation and star formation. A vast wave of hot gas spanning some 200,000 light-years formed in the Perseus cluster after that a small galaxy cluster about a tenth its mass grazed by and caused its vast supply of gas to slosh around illustrating that interactions occur between galaxy clusters Perseus Galaxy Cluster. Some galaxies have been rejuvenated with a ring of stars formation as that might be explained by a continued accretion of intergalactic gas by a galaxy. The pace brakes then and formation declines until now, thus featuring a striking time similarity with the time at when the pace of the expansion of the Universe is accelerated. The star formation inside galaxies is following the hydrogen track, meaning that stars forms, at the outreaches of galaxies included, there where there is hydrogen gas. Dust structures of filaments, on a other hand, and round or irregular clouds, or vertical columns, loop-like structures or vertical cones are likely playing a role into the ejection of gas and dust from the galactic plane of spiral galaxies transporting the interstellar medium to large distances away. Powerful stellar winds from supernovae are initiating the process. Active Galactic Nuclei (AGNs) are seen keeping being frequent inside galaxies until the Universe reaches 60 percent of its age as such objects become rarer after that time (AGNs are galaxies with a massive black hole at their center, expelling gaz from the center under the form of two polar cones from the galaxy. The Seyfert type galaxies are a category of the AGNs, with the area immediately around the black hole which may shine powerfully with radiation coming from the material falling in as their brightness is comparable to that of our entire Milky Way Galaxy. Such galaxies are accounting for 10 percent of galaxies existing today. In some Seyfert galaxies, a dusty ring may lie perpendicular to the plane of a elliptical galaxy as they might be linked to two jets flowing material out, a sign of how the black hole is speeding up and sucking in gas from nearby space). Blue Compact Dwarf (BCD) galaxies, like NGC 5253 for example, are galaxies which harbor very active star-formation regions in spite of their low dust content and comparative lack of elements heavier than hydrogen and helium, which are usually the basic ingredients for star formation. The molecular clouds in BCD galaxies are quite similar to the pristine clouds that formed the first stars in the early Universe, which were devoid of dust and heavier elements. Today Universe is mainly composed of dwarf spheroidals, dwarf and giant ellipticals. Most galaxies observed are either in their spiral, or their elliptical shape as few are during the transition phase between both. As mergers are the main evolutive factor to galaxies, that might hint to that transition phase is short-lived. That is easily explained by that a merger between two galaxies yields a burst of star formation which quickly exhaust the available gas. Maybe too a merger reactivates the black holes in both galaxies, which emit shocks and jets as that also exhaust the gas available -it is expelled out from the galaxies or permanently stirred. Both processes as they swiftly exhaust any gas available to star formation make that the transition phase likely is unfolding on short time scales

Dwarf Galaxies in The Halo of Large Galaxies
Faint dwarf galaxies which lie in our Milky Way Galaxy' backyard or other large galaxies' are thought to be some of the tiniest, oldest, and most pristine galaxies in the Universe. Such galaxies are dominated by dark matter as a swarm of dark matter clumps around our Milky Way as some chunks become massive enough to obtain gas from the intergalactic medium and trigger star formation, eventually creating dwarf galaxies. Dwarf galaxies formed stars during the first billion years after the Universe had been born as a shutdown of star formation was triggered when first stars processed the reionization phase; that also stripped dwarf galaxies from their gas. That also could help explain the so-called 'missing satellite problem,' where only a few dozen dwarf galaxies have been observed around the Milky Way while computer simulations predict that thousands should exist as that is also true for the Universe, generally. Distribution of dark matter within dwarfs is also quite puzzling (the 'cuspy halo' problem). One possible explanation is that there has been very little, or even no star formation in the smallest of these dwarf galaxies, making them difficult to detect. The stellar populations in these fossil galaxies range from a few hundred to a few thousand stars both fainter and brighter than our Sun as they contain 10 to 100 times more dark matter compared to ordinary matter

The in-between phase between a spiral and a elliptical galaxy is refered to by astronomers like a 'lenticular' galaxy, which possesses features of both, with a central bulge, a bar, a thick disk -- they are disk-shaped -- and an outer ring as in contrast to typical spiral galaxies they have used up most of the interstellar medium and the star formation rate is very low like in elliptics, and they have no spiral arms. Lenticulars are widespread. Lenticulars also result from galaxy mergers as their Tully–Fisher relation, which also characterizes spiral galaxies --a observed relationship between luminosity and rotation velocity -- however settles slowly within 4 to 7 billion years after the merger. The stage somewhere between a lenticular and a spiral is called a hybrid galaxy. Lenticular are hosting aged stars like ellipticals and have a disk like a spiral. They differ from ellipticals because they have a bulge and a thin disk, but they are different from spirals because lenticular discs contain very little gas and dust, and do not feature the many-armed structure that is characteristic of spiral galaxies. Sometimes a polar ring of material may be encircling the galaxy’s core and have a series of filaments made of dust at right angles to the disk. Lenticulars are of the S0 class of galaxies. Such disk galaxies have used up the majority of their gas and dust. As a result, they experience very little ongoing star formation and consist mainly of old and aging stars. Both classes are also deemed 'early-type' galaxies, because they are evolving passively. As ellipticals however endured active phases in the past, S0 galaxies are either aging and fading spiral galaxies, which never had any interactions with other galaxies, or they are the aging result of a single merger between two spiral galaxies in the past. Ellipticals are twice as numerous today than 9 billion years ago as the massive brand began like spirals and a supermassive black hole eventually removing raw matter needed for star formation. Elliptical do not spin. A quarter of ellipticals seem to have rapidly rotating disks of gas at their centers. Some ellipticals may be part of a unusual class of galaxies with a diffuse core filled with a fog of starlight where there would normally be a concentrated peak of light around a central black hole. The core's size in this case is much larger. Such a scattered core might be due to a pair of merging black holes disturbing the centrality of stars, or that the merging black holes were ejected from the core leaving the stars without a anchor. Black holes are still active and growing in most galaxies except in ellipticals. They are the relics of the ancient quasars. Young building-block galaxies still appears, being as young as 500 million years. One of them is located 45 million light-years from our Milky Way Galaxy. Barred spiral galaxies form about two thirds of all spiral galaxies, including the Milky Way. Barred galaxies are boxy, X shaped as it remains unclear how and when these boxy bulges formed. They began forming some seven billion years ago and their formation is related to that of galactic bars, which are two billion years older. Stars inside bars orbit the galactic centre in complex, dynamic ways, with an array of vertical motions that likely contribute to the boxy morphology. Recent studies suggest that bars may be a common stage in the formation of spiral galaxies, and may indicate that a galaxy has reached full maturity. Galactic bars also are thought to act as a mechanism that channels gas from the spiral arms to the center, enhancing star formation, which is typically more pronounced in the spiral arms than in the bulge of the galaxy. Another mainpoint is that mergers are allowing for a transition between vigorous gas-rich spirals -fulled with blue, young stars and quiescent ellipticals -astronomers call 'red and dead' due to the reddish glow of their aging stars. The process that drives the dramatic transformation from spiral galactic youth to elderly elliptical is the rapid loss of cool gas, the fuel from which new stars form. Short-lived blue stars that form right after the merger soon turn supernova explosions can start the decline in star formation as they trigger a fast ouflow of heated gas which begin to banish the reserve of star formation's cold one, and then shock waves from the supermassive black hole finish the job as the supermassive black hole that reside in the center of the resulting galaxy can flare up when engorged by gas during the galactic merger and yield polar jets of matter. Shock waves from these jets heat up and disperse the reservoirs of cold gas thus preventing new stars from taking shape and bringing to a elliptical. Such waves are rushing outward from the galactic center at a velocity of nearly two million miles per hour (nearly 3.2 millions of kilometers per hour) as they reach the outer portions of a galactic merger in about 10 million years. Such quenching of star formation probably occurs in just a billion years. That's not very long compared to the 10-billion-year age of a typical big galaxy. Galaxies which have moved down to the center of their cluster have been stripped of their gas, hence can not participate anymore into any star formation process. Some have even been completely disrupted, spilling their stars and gas into the intergalactic space. Color is a way of gauging galaxies age, with lively, young galaxies looking bluish to our eyes due to the energetic starlight of their new, massive stars as elderly galaxies instead glowing in the reddish hues of their ancient stars. Clusters nowaday are containing between hundreds and thousands galaxies, with temperatures in the cluster ranging 10-100 million degrees. The most massive of galaxy clusters hold the equivalent of a million billion suns worth of mass. Pools of hot gas are permeating roughly 14,000 smaller clusters of galaxies. Interactions occur among the galaxy clusters. The M87 galaxy, in the Virgo Cluster, has, for example, his supermassive black hole having a control over the evolution of the galaxy as its reach further extends even farther into the entire cluster which M87 belongs too. The black hole is blasting away, by interval, a powerfull mass of the infalling gas coming from the Virgo Cluster into the galaxy, preventing the formation of millions stars. That activity, on the other hand, is resounding too into the cluster with such blasts of matter rising into the cooler gas composing the cluster's interior. The background hot gas in a galaxy cluster, generally, cools and falls toward the cluster's galaxies center where it continues to cool even faster and form new stars. Galaxy mergers are keeping now, even between mature galaxies, ending up in galaxies which may reach as big as ten times the size of our Milky Way Galaxy. Galaxy mergers are heralded by bridges of hydrogen gas linking both actors, as a tidal tail of gas and stars, from intense gravitational disruptions, typically precedes a galaxy merger. Mergers may be of the type gas-rich, with stars formation, or gas-poor, with none. Dwarf galaxies may still be episodically seen colliding close to us, at 166 million light-years for example, providing for opportunities of better understanding most ancient collisions which formed large galaxies from smaller building blocks. A last point: dwarf galaxies as seen in the Virgo Cluster might find their origin 6 billion years ago. Galaxies, apart stars, are containing too gas, which allow for the formation of stars. Such gas gather into the so-called interstellar or 'molecular' clouds. Those clouds, inside a galaxy, are subject to a variety of forces like the rotation of a galaxy, the radiations and particles jets emanating from nascent stars, or magnetic fields. Not to mention the impact of the powerful relativistic polar jets shot away from the biggest of the supermassive black holes like a proof of the continued interaction between a galaxy and the supermassive black hole it holds, the average ones also interact with a galaxy's formation with material blown away, as opposed to the one falling into. Jets thus play an important but poorly understood role in the formation and evolution of galaxies, like changing at times with star formation. The speed of the material is of about a million miles/h (1.6 million km/h) as it is transported to about 3,000 light years away from the galaxy's center. The wind may carry enough energy to heat the surrounding gas and suppress extra star formation. In the future, our own Galaxy's black hole may undergo similar activity, helping to shut down the growth of new stars in the central region of the Milky Way. A mysterious infrared glow from the Milky Way and other galaxies, as discovered in the 1970’s and 1980’s, radiating from dusty regions in deep space is composed of polycyclic aromatic hydrocarbon (PAH). PAHs in space are probably produced by carbon-rich, giant stars. Galaxy dust, on a other hand, is made primarily of polycyclic aromatic hydrocarbons, which are found on Earth as soot

->Barred Spirals, Another Way to Have the Galaxies Evolve after 7 Billion Years Ago!
Barred spirals seems to be the mark of the matureness of the galaxies' evolution, with they being less numerous before 7 billion years ago. Less than 20 percent of the galaxies then possess a bar, against 70 percent of the galaxies today, as the bars mostly formed after 7 billion years ago. The bar however is forming among the small, low-mass galaxies as, with the most massive ones, the percentage of galaxies with a bar remain the same today than in the past. That might hint to two different ways the galaxies evolve: the most massive forming their stars early and fast and then turning into ellipticals, as the low-mass galaxies might form their stars at a slower pace -the same pace they are forming their bar
A bar of a galaxy results from that the stellar orbits in a galaxy become unstable and eventually the eccentricity of their orbits locks into a stable location, generating a bar of stars accross the spiral galaxy. The bar likely too is the responsible for aggregating a large amount of gas to the center of a galaxy, thence a higher star formation, a central bulge and the supermassive galactic black hole! The bars might well be the other most important factor of the evolution of the galaxies, after the mergers between then. Our own Milky Way Galaxy is a massive barred spiral, with the bar forming early

->It's the Interactions in the Galaxy Clusters Which has the Spirals Turn Ellipticals!
The half of the galaxies in the Universe today are gas-poor, few forming new stars ellipticals, with the other half keeping being spirals and irregulars with much gas and a high formation rate. It looks like it's likely the interaction in the galaxy clusters which lead to that. 7 billion years ago, one to 5 galaxy only was gas-poor. As the spirals are interacted by their cluster's gravity, this lead to them stripped of their gas -and even stars, which end 'homeless' and scattered in the cluster. The process is thought to last about 1 billion years with the elliptical eventually settling near the clusters' center

->The Case of the Globular Clusters
The collapse of dark matter to the center of galaxy clusters might help to a larger star formation rate in the galaxies at that place than at the outskirts, forming globular clusters by the same occasion. With the interactions inside a cluster, the galaxies are 'stealing' their globular clusters between them as such globular clusters exist around dwarf galaxies also

More Data

• a recent study published in 'Nature' is showing that star formation peaked about 8.7 billion year after Big Bang with a disparity between low-mass (peak at 11.7 billion years after Big Bang only) and high-mass (peak at 3.7 billion years after Big Bang) galaxies. All this is pointing to a formation further in time than previously thought (peak was thought at Big Bang plus 5.7 billion years). Rate is downplayed too: "Nature" study sees it at 10 times today's rate as previous studies were at 15-20 times
• about the collisions between galaxies, such galaxies in a collision act, are called luminous infrared as the result is a monster galaxy known as an 'ultra-luminous infrared galaxy' or Luminous Infrared Galaxies, LIRGs, thousands of times as bright in infrared as our Milky Way!
• giant and dwarf ellipticals are now seen to be equivalent as far as their stars distribution and their formation is concerned
• ellipticals seem to have less dark matter halos; an explanation could be that they often gather in clusters hence frequent collisions might strip halos
• evidence of accretion unto ellipticals is better provided in X-rays than in optical as the latter quickly fades into the stars background of the galaxy
• accretion process is disrupting cannibalized galaxies by tidal forces. This yields long gas trails which in turn are producing massive, short-lived, stars swiftly turning supernovae, black holes, and neutron stars
• a thoroughful understanding of clusters history from earlier times to today is underway. This will be made possible by combining different wavelengths using e.g. Hubble for visible, Chandra for X-rays, VLT for distances and chemical composition accurate measurements, or near-infrared for assessment of star formation rate. An example of clusters impact about galaxy history is they are colliding together bringing a decline in the number of spiral galaxies. As spirals are very numerous in the early Universe, they are taking the brunt of such collisions
• in a seemingly paradoxical agreement with the acceleration of the expansion of the Universe due to the dark energy, one sees that the galaxy clusters, beginning 5,5 billion years, don't come to more mass anymore. The dark energy thus would act and limit the gravitational attraction of the clusters!
• about how much galaxies are visible nowadays in the Universe, it might well, according to a study by the European ESO, in Chile, in 2010, than a tenfold increase need to be applied. Where 10 galaxies have been observed until now, there could be a hundred instead! That is appearing from the fact that galaxies until now have been searched through the thin range of light of the hydrogen present in the galaxies, called the Lyman-alpha line. Some critics however have pointed to that the Lyman-alpha light never makes it to Earth as being absorbed by gas and dust of the Universe. Looking at a same patch of sky in the Lyman-alpha hydrogen and in the H-alpha line of the hydrogen, researchers found that the galaxies seen only in the H-alpha hydrogen might have looked dark to telescopes working in the Lyman-alpha. A far more accurate representation of the Universe could emerge from that findings